Employer Withholding Tips/unfair Wages

Hey, I just had a quick question involving my employer

I’ve been working as a server as a very part time job for almost a year at this restaurant and have never gotten a single tip. I never question it and always put the cash in the tip jar like my employer tells me to, which goes to the kitchen. Not to us. Aside from that, recently I’ve worked the same amount of hours but am noticing less and less money being paid to me via check. For example, I worked 10 hours back in may and got paid $210. I worked 10 hours in a month recently and got paid $84. My friend, also a server, when he got his paycheck for $109 for the month, realized that she (my employer) had literally cut the check in half, as the amount should have equated to $220. She promised him she’d pay it, although these things happen often and I’m wondering if I should speak out. If so, how would I do it without getting fired and is any of this actually illegal?

P.S. She said she gave away end of year bonuses and I texted her a reminder two weeks ago as I haven’t received mine. She has yet to recognize my message much less reply.

If yall could provide some insight, it would be much appreciated. By the way, this is in Wisconsin, USA and my friend and I are both sixteen