Can I Ask a Cop If I’m Under Arrest?

Yes.

But the cop will avoid an answer.

They will dodge this question as long as possible.

If the officer was trying to entice you to make a voluntary statement you just put him on notice that it's time to fish or cut bait. And if you are being baited it's best to know that before you start telling a police officer everything he needs to arrest you.

All this sounds very mean spirited and cynical. It is neither, it is good advice

Believing for one moment you can talk a cop out of arresting you makes as much sense as giving a Burger King coupon to a raptor.