Couple of suggestions for code

1_TidiedCode.m

- (void)clickedonPoint {
    self.m_mapView.touchDelegate = self;
    
    self.m_sketchLayer.geometry = [[AGSMutablePoint alloc] initWithSpatialReference:self.m_mapView.spatialReference];
    // Not sure why you have a sketchLayer here.
    // However, if you do have one, you need to set the mapView's touchDelegate to the sketch layer.
    // See https://developers.arcgis.com/ios/swift/guide/sketch-layer.htm#GUID-4CF8925A-B8B9-4656-AE3D-51DD126234CA
}

-(void)mapView:(AGSMapView *)mapView didClickAtPoint:(CGPoint)screen mapPoint:(AGSPoint *)mappoint features:(NSDictionary *)features {
    self.m_queryTask = [AGSQueryTask queryTaskWithURL:[NSURL URLWithString:CurrentLayerURL]];
    // If the layer at CurrentLayerURL is already in the map, you don't need to query to get results, you can just
    // get the features out of the "features" parameter that's being passed in. See 3_BestSuggestionIfLayerIsInMap.m
    
    self.m_queryTask.delegate = self;
    AGSQuery *currentQuery = [AGSQuery query];
    
    currentQuery.spatialRelationship = AGSSpatialRelationshipIntersects;
    currentQuery.outFields = @[@"*"];
    currentQuery.returnGeometry = YES;
    currentQuery.outSpatialReference = self.m_mapView.spatialReference;

    AGSEnvelope *env = [AGSEnvelope envelopeWithXmin:mappoint.x - 10.0
                                                ymin:mappoint.y - 10.0
                                                xmax:mappoint.x + 10.0
                                                ymax:mappoint.y + 10.0
                                    spatialReference:self.m_mapView.spatialReference];
    // I'm not sure what you're doing with WKIDs, but you should pass in a valid SpatialReference

    currentQuery.geometry = env;
    
    self.m_lastClickedMapPoint = mappoint; // Keep the search point for searching later.
    
    [self.m_queryTask executeWithQuery:currentQuery];
}

-(void)queryTask:(AGSQueryTask *)queryTask operation:(NSOperation *)op didExecuteWithFeatureSetResult:(AGSFeatureSet *)featureSet {
    if (featureSet.features > 0) {
        NSArray *orderedFeatures = [featureSet.features sortedArrayUsingComparator:^NSComparisonResult(id  _Nonnull obj1, id  _Nonnull obj2) {
            AGSGraphic *f1 = obj1, *f2 = obj2;
            AGSGeometryEngine *ge = [AGSGeometryEngine defaultGeometryEngine];
            double d1 = [ge distanceFromGeometry:self.m_lastClickedMapPoint toGeometry:f1.geometry];
            double d2 = [ge distanceFromGeometry:self.m_lastClickedMapPoint toGeometry:f2.geometry];
            
            return d1 < d2 ? NSOrderedAscending : (d1 > d2 ? NSOrderedDescending : NSOrderedSame);
        }];
        
        AGSGraphic *closestFeature = orderedFeatures[0];
        
        // Do something with the closest feature here...
    }
}

2_BetterSuggestion.m

- (void)clickedonPoint {
    self.m_mapView.touchDelegate = self;
}

-(void)mapView:(AGSMapView *)mapView didClickAtPoint:(CGPoint)screen mapPoint:(AGSPoint *)mappoint features:(NSDictionary *)features {
    self.m_queryTask = [AGSQueryTask queryTaskWithURL:[NSURL URLWithString:CurrentLayerURL]];
    
    self.m_queryTask.delegate = self;
    AGSQuery *currentQuery = [AGSQuery query];
    
    currentQuery.spatialRelationship = AGSSpatialRelationshipIntersects;
    currentQuery.outFields = @[@"*"];
    currentQuery.returnGeometry = YES;
    currentQuery.outSpatialReference = self.m_mapView.spatialReference;

    AGSGeometry *searchGeom = [[AGSGeometryEngine defaultGeometryEngine] bufferGeometry:mappoint byDistance:10];
    
    currentQuery.geometry = searchGeom;
    
    self.m_lastClickedMapPoint = mappoint; // Keep the search point for searching later.
    
    [self.m_queryTask executeWithQuery:currentQuery];
}

-(void)queryTask:(AGSQueryTask *)queryTask operation:(NSOperation *)op didExecuteWithFeatureSetResult:(AGSFeatureSet *)featureSet {

    if (featureSet.features > 0) {
        NSArray *orderedFeatures = [featureSet.features sortedArrayUsingComparator:^NSComparisonResult(id  _Nonnull obj1, id  _Nonnull obj2) {
            AGSGraphic *f1 = obj1, *f2 = obj2;
            AGSGeometryEngine *ge = [AGSGeometryEngine defaultGeometryEngine];
            double d1 = [ge distanceFromGeometry:self.m_lastClickedMapPoint toGeometry:f1.geometry];
            double d2 = [ge distanceFromGeometry:self.m_lastClickedMapPoint toGeometry:f2.geometry];
            
            return d1 < d2 ? NSOrderedAscending : (d1 > d2 ? NSOrderedDescending : NSOrderedSame);
        }];
        
        AGSGraphic *closestFeature = orderedFeatures[0];
        
        // Do something with the closest feature here...
    }
}

3_BestSuggestionIfLayerIsInMap.m

- (void)clickedonPoint {
    self.m_mapView.touchDelegate = self;
}

-(void)mapView:(AGSMapView *)mapView didClickAtPoint:(CGPoint)screen mapPoint:(AGSPoint *)mappoint features:(NSDictionary *)features {
    // Use the name of the layer from when it was added with AGSMapView:addMapLayer:withName
    NSArray *featuresOnLayer = features[CurrentLayerName];
    
    if (featuresOnLayer && featuresOnLayer.count > 0) {
        // Now sort the features on order of distance from the map point.
        NSArray *orderedFeatures = [featuresOnLayer sortedArrayUsingComparator:^NSComparisonResult(id  _Nonnull obj1, id  _Nonnull obj2) {
            AGSGraphic *f1 = obj1, *f2 = obj2;
            AGSGeometryEngine *ge = [AGSGeometryEngine defaultGeometryEngine];
            double d1 = [ge distanceFromGeometry:mappoint toGeometry:f1.geometry];
            double d2 = [ge distanceFromGeometry:mappoint toGeometry:f2.geometry];
            
            return d1 < d2 ? NSOrderedAscending : (d1 > d2 ? NSOrderedDescending : NSOrderedSame);
        }];
        
        AGSGraphic *closestFeature = orderedFeatures[0];
        // Do something with the closest feature here...
    }
}

4_WithConsoleOutput.m

- (void)clickedonPoint {
    self.m_mapView.touchDelegate = self;
}

-(void)printClickFeatures:(NSDictionary *)features {
    for (NSString *layerName in features.allKeys) {
        AGSLayer *layer = [self.m_mapView mapLayerForName:layerName];
        NSURL *layerURL = nil;
        if ([layer respondsToSelector:@selector(URL)]) {
            layerURL = [layer performSelector:@selector(URL)];
        }
        NSArray *featuresForLayer = features[layerName];
        NSLog(@"There are %lu features returned on layer '%@'. URL: %@", featuresForLayer.count, layerName, layerURL);
    }
}

-(void)mapView:(AGSMapView *)mapView didClickAtPoint:(CGPoint)screen mapPoint:(AGSPoint *)mappoint features:(NSDictionary *)features {

    [self printClickFeatures:features];

    // Use the name of the layer from when it was added with AGSMapView:addMapLayer:withName
    NSArray *featuresOnLayer = features[CurrentLayerName];
    
    if (featuresOnLayer && featuresOnLayer.count > 0) {
        // Now sort the features on order of distance from the map point.
        NSArray *orderedFeatures = [featuresOnLayer sortedArrayUsingComparator:^NSComparisonResult(id  _Nonnull obj1, id  _Nonnull obj2) {
            AGSGraphic *f1 = obj1, *f2 = obj2;
            AGSGeometryEngine *ge = [AGSGeometryEngine defaultGeometryEngine];
            double d1 = [ge distanceFromGeometry:mappoint toGeometry:f1.geometry];
            double d2 = [ge distanceFromGeometry:mappoint toGeometry:f2.geometry];
            
            return d1 < d2 ? NSOrderedAscending : (d1 > d2 ? NSOrderedDescending : NSOrderedSame);
        }];
        
        AGSGraphic *closestFeature = orderedFeatures[0];
        // Do something with the closest feature here...
    }
}

I'm not sure why you are using a Sketch Layer. And I assume that the layer is already on the map. If that's the case, go with example 3 here.

I have tried to clean up some of your code in example 1.

In example 2, I still use the QueryTask, but use a buffer instead of an envelope.

However, if the layer with the features you want is on the map, use example 3.