"He said he was calling from Landsford Park, wherever that is."
Even though the first man says where he is - Landsford Park - the name 'Landsford Park' and hence, its whereabouts, is completely unknown to the speaker, and so he is absolutely none the wiser as to where this person is located (if he or somebody is supposed to be going to meet him/pick him up). He is saying the equivalent of "God knows where that is." - 'wherever on God's Earth that may be because I certainly don't know."
"He said his name is Lord Darnley, whoever that is (when he's at home)."
"He looks like a salesman, and says he's from "Famous Fabs" - whoever the hell they are!
Do you mean that It is not correct to use "wherever"?
Do you mean it should be "whatever"?
No, the usage of "wherever" is perfectly fine there. I was just being an upstart, impudent American.
Say two people are arguing (not very heatedly or acrimoniously). One takes his time stating his case, but the other doesn't want to waste time or energy on the argument so he dismissively says "Whatever". (It's relatively recent, but it has really caught on.) It is definitely informal (as most speech is). It expresses mild disagreement (but I am not disagreeing with anything in this thread).