I have a radiant PEX tube heating system in my garage floor. Since I didn't mark them when it was poured, is there a way I can first locate and then safely drill into the floor to place expansion bolts for a car lift?

Not that I know of. You are going to have to hand chisel, slowly and carefully.

They can do thermal imaging, similar to what they use to find heat leaks in houses. It measures infrared. Google "Thermal floor imaging ".