How do you find out who gives senior discounts for fifty-five?

You basically just have to ask around. Just ask politely for the senior discount. If they have one, they will give you it, if they don't, well, then they won't. I'm not a senior yet, but I went through the same thing being a student, I found out that some local restaurants give "student" discounts ;) Goodwill Industries theft shop, and a local Wendy's will give student's a 10% off discount. It's really nice, especially in this bad economy.