One of my frustrations with Zotero is that there is no easy way to list all the collections in which a file is stored. This is my band-aid of a solution. The code can be run under Tools > Developer > Run Javascript using "Sync" mode.

lookupZoteroCollections.js

// Instructions: 
// (1) Highlight file of interest. 
// (2) Run code in Zotero's JavaScript console (found under Tools > Developer > Run Javascript) in sync mode.

function collections_output() {
    zp = Zotero.getActiveZoteroPane()
    items = zp.getSelectedItems()
    collection_ids = items[0]["_collections"]
    
    collections_cache = Zotero.Collections._objectCache
    
    return_string = items[0]["_displayTitle"]
    return_string += "\n\nCollections: \n"
    
    for (i = 0; i < collection_ids.length; i++) {
        return_string += "("
        return_string += i+1
        return_string += ") "
        return_string += collections_cache[collection_ids[i]]["name"]
        if (i + 1 != collection_ids.length) {
            return_string += "\n"
        }
    }

    return return_string
}

collections_output()

Using Zotero's Built-In CTRL-Key Option:

Using lookupZoteroCollections.js

Great, thank you!

Really helpful! Thank you!