Generated by SassMeister.com.

SassMeister-input-HTML.html

<p class="output">
  The output number is
</p>

SassMeister-input.scss

// ----
// libsass (v3.2.5)
// ----

/**
*
* Is there any way to fetch the last key and a specific key inside it?
*
**/
$map: (
  key-1: (
    first: true,
    number: 1,
  ),
  
  key-2: (
    first: false,
    number: 2,
  ),
);

// Map last key function by James Steinbach
@function map-last-key($map) {
  $keys: map-keys($map);
  @return nth($keys, length($keys));
}

// Get a specific value from the last nested map
@function map-last-value($map, $sub-key) {
  $last-value: map-get($map, map-last-key($map));
  @return map-get($last-value, $sub-key);
}

// Map fetch function by Hugo Giraudel
@function map-fetch($map, $keys) {
  @each $key in $keys {
    $map: map-get($map, $key);
  }
  @return $map;
}

.output:after {
  last-key: map-last-key($map);
  last-value: map-last-value($map, number);
  content: '' + map-fetch($map, key-2 number);
}

SassMeister-output.css

/**
*
* Is there any way to fetch the last key and a specific key inside it?
*
**/
.output:after {
  last-key: key-2;
  last-value: 2;
  content: "2";
}

SassMeister-rendered.html

<p class="output">
  The output number is
</p>