When Prince used to perform Why You Wanna Treat Me So Bad live in the early 80s, who took the great guitar solos during those shows, Prince or Dez or both of them?

A bit of both. Prince started off the solo, but when there is the harmony being played a few notes higher, both Prince and Dez play. I'm sure you can find a video of it on YouTube, I'm sure I've seen one.

guitar solo is played by prince,only at the end of solo(same as studio) 2 guitars are playing together.but guitar solo is by prince

i thought Prince did all the instruments then.

Prince did all the instruments on the record, but they both did it live. It's pretty much impossible otherwise.