How can I list all folders that contain files with a specific file extension? I want a list that shows the parent folders of all files with a .nef extension.

Question

not the total path to the folder containing the files but rather just a parent folder one level up of the files.
So file.nef that's in folder 1 that's in folder 2 that's in folder 3... I just want to list folder 1, not 2 or 3 (unless they contain files themselves in their level)

Answer 1

find $HOME -iname '*.nef' 2>/dev/null | awk -F '/'   'seen[$(NF-1)]++ == 0 { print $(NF-1) }'
This will print just one occurrence of directory
The 'find' command files ALL *.nef files under your home directory (aka Folder)
The 2>/dev/null throws away any error messages from things like "permissions denied" on a protected file or directory
The 'awk' command extracts the parent directory and keeps track of whether it has displayed that directory before
-F '/' tells awk to split fields using the / character
NF is an awk variable that contains the number of fields in the current record
NF-1 specifies the parent directory field, as in the last field is the file name and minus one if the parent directory
$(NF-1) extracts the parent directory
seen[] is a context addressable array variable (I choose the name 'seen'). That means I can use text strings as lookup keys.  The array is dynamic, so the first time I reference an element, if it doesn't exist, it is created with a nul value.
seen[$(NF-1)] accesses the array element associated with the parent directory.
seen[$(NF-1)]++ The ++ increments the element stored in the array associated with the parent directory key AFTER the value has been fetched for processing.  That is to say the original value is preserved (short term) and the value in the array is incremented by 1 for the next time it is accessed.
the == 0 compares the fetched value (which occurred before it was incremented) against 0.  The first time a unique parent directory is used to access the array, a new element will be created and its value will be returned as 0 for the seen[$(NF-1)] == 0 comparison.
On the first usage of a unique parent directory the comparison will be TRUE, so the { print $(NF-1) } action will be performed.
After the first use of a unique parent directory name, the seen[$(NF-1)] access will return a value greater than 0, so the comparison will be FALSE and thus the { print $(NF-1)] } action will NOT be performed.
Thus we get just one unique parent directory name no matter how many *.nef files are found.  Of course you get only one unique name, even if there are several same named sub-directories but in different paths
You could put this into an Automator workflow using the "Run Shell Script" actions.