Skink does not recognize captured Ash Ghoul souls in soul gems he gave my character. He says PC can't fool him and that he has no suitable soul gems on him.
My PC was carrying many soul gems, so I removed them all from his inventory and retained only the Ash Ghouls gems. That did not work either, even after having PC sleep for 3 days before returning to Skink.
I tried to use a console command to fix it, but don't really know what I am doing.
Any suggestions?

You have to kill one specific
You have to kill one specific Ash Ghoul found in Yakin. He carries the soulgem you need. Capturing specific souls with soulgems isn't possible in Oblivion.