How can I identify and clear specific cache files on iMac?

Restart in Safe Mode.

This will perform Clear System Cache files.

You do realize, the System Cache files will be recreated and the System Requires

If you mean some Other Caches files ?

You are going to have to specific

You do realize, the Cache files for other applications will also l be recreated as the applications needs

Launched applications store their caches in your /Users/username/Library/Caches folder. These are the only caches that you would have permission to and rarely need to manage. I don't bother.

Your only means of managing System caches would be via booting into Safe Boot mode as has already been mentioned. Again, I don't bother as for the most part, the System takes care of that.

If Lack of Empty Space is the really issue ?

You are better off looking elsewhere for the reason already mentioned by both posting

Do let us know if this is so

Perhaps we can point you in the right direction