This is kind of open ended. What do you mean? Typically, i get my blood taken once a year, go over it with my doctor, and then go from there. When I started TRT I had a bunch of blood tests, maybe every month (ever other?) to dial in the amount of testosterone I needed.
I only get more blood tests if something is irregular - so, for instance, my liver values were off, so my doctor is having me retest next month.
That's generally. If you're talking about a cycle, I would take a test before and then midway through. If things look expected, I'd take another test about a month after PCT.