What does the title "Whose line is it anyway?" mean?

Whose line is it anyway? is a comedy show in which participants are given a theme and they are supposed to come up with an act according to the theme given to them.

According to Oxford Dictionary, one possible meaning of anyway is to ask a question, like

What are you doing here anyway?

but I am not able figure out the meaning of anyway in this expression. Maybe it is because I am not able to imagine the context it has been said in.

What is the explanation?

As noted in the History section of wikipedia's article about the Whose Line Is It Anyway? show,

Indeed the title of the show itself is a comedic riposte to another radio show, What's My Line, merged with the title of a 1972 teleplay (and eventual theatrical play) Whose Life Is It Anyway?.

The adverb anyway (with conjunctive sense “regardless; anyhow”) when used in questions like “Whose line is it anyway?” or “What are you doing here, anyway?”, has a sense of “other questions aside”. That is, “What are you doing here, anyway?” is more or less equivalent to “Ignoring other questions, what are you doing here?”

Anyway in the context you provided, means regardless of other things or leaving other things aside. So what are you doing here anyway? means that I am not interested in whatever other things you are doing or may have. I just want to know what you are doing here.

I believe the origin was a hoary theatrical anecdote about a play that had been running too long, so the actors completely forgot what to say in the middle of a scene. The prompter hissed the line, but was ignored; repeated it at increasing volume, and was asked by one actor "Yes, we heard you; but whose line is it anyway?"