I would say somewhere between 0 and 2 if you’re using a hardware-based hypervisor because the ability to address certain host hardware pretty much stops after Host>VM>VM (there are caveats), and the returns are immediately diminished after the first.

If using a software Hypervisor, you can probably go as far as your resources would let you, but I’d guess about 3 or 4 layers deep on most commercial hardware because the required resources the HV needs to track all the layer translations will balloon quite quickly.