Find out a reserve

You can ask, but if someone has paid the extra fee to have a hidden reserve, then it sort of defeats the point. Encouraging people to bid is the main reason people pay to have a hidden reserve.

You can't. If the seller has paid for a hidden reserve then that's what it is. Hidden.

You can ask the seller what it is. Up to them if they reveal it or not.

The other way. Not really moral, but I have seen it happen. Place a ridiculously large bid, which will reveal the reserve, then ask Trade Me or the seller to remove the bid because it was an "error"

How to pay for a hidden reserve