How do I know if somebody selects my answers useful on ask.com iPhone app?
Click on My Profile at the bottom.
unfortantely, the app doesn't support that feature yet, sorry.
When some one selects your answer and click for golden star for helpful, or for fun, when you are live or working on the site you get pop up names of those who select them. But if you want to see afterwards that software is not available at present.