Can someone please explain this term/slang “问个P” Is it related to this phrase: 问个屁/問個屁
Yes, it's 问个屁. P -> 屁. 

问个屁 means Don't ask!. It indicates that you are annoyed by the questioner. It's a way to block their questions to annoy you any further. 

It's a ruder way to say 别问了！