In English, parents often scold their kids by saying "How many times do I have to tell you not to ...."?
It's a rhetorical question, intended to express exasperation at the repeated (and apparently futile) admonishing. It's not a literal query of the number of times scolded. In the Japanese example above, the feeling is similar. The questioner is not asking for a literal measurement.
どこまで勝手をすりゃあ、気が済むってんだ!
Just how selfish do you need to be in order to feel satisfied.
In today's parlance we would say, "Selfish, much?"