Well as far as I know there are many programs that implement 20 reppers.
The originale 20 rep squat program had you do
1x20 squats
1 set of pullovers
1x15 stiff legged deadlifts
DC training also somewhat implements them under the name of widowmakers
Hamstring: work 1 Rest pause set or a couple of straight sets (based on safety)
1 heavy squat set + 1 20 reppers (not necessarily on squats)
However keep in mind that this was designed for Advanced people.
I would argue that if you don’t have any issues/injury (as I assume since you don’t mention any of them) you may do something along the line of
Calf work (working them before Will provide stability and improbe depth)
1x20 squats
And some hamstring work later (2-3 sets of leg curls might suffice, expecially of you’re somewhat working your erectors with bent over rows or ohp during upper days)
The standard response to anyone wanting to do 20 rep squats is to go ans but a copy of the Super Squats book and read it.
But assuming you dont want to do that, it would be good to get a little more information.
How long have you been training? What are your goals ? How many days a week are you looking to train ? Do you train at home or in a commercial gym ? Any injuries or movements you cant do ?
Current strength level for squat - max 5 reps ?