T-bol,
My favorite oral, although I haven't tried that GP oral tren yet but suspect thats a little too harsh for a guy my age.

The answer to your question depends on his goals.

Some people take just 10mg a day for its binding effects on SHGB which in turn allows for more free testosterone. Others use 10 mg a day for "cruising" in between cycles to maintain gains.

Your friends weight should be considered too. Obviously a 250 lb power lifter might need a little more than a 189lb - 199lb older guy like me. (On and off)

I have found 20 mgs to be enough to notice some pumps, 30 mgs to really notice those pumps, 40 mgs to start causing me to cramp painfully up if I try to scratch my own back.

If he's around 200 give or take twenty pounds, tell him to start out with 20 mgs and after about ten days he can up it to 30 mgs. If this person has a few cycles under his belt, 30 mgs might be a good place to start imo, to get the full benefits of OT, as I call it. If he starts to get painful back pumps back it off 5 mgs until he finds his sweet spot, or increase as the case may be. The painful back pumps, or sever cramping is a sign to cut down.
30mgs is a good place to start. Give it a full two weeks, he'll feel it when he can only do just over half the reps he usually does because the pump is so hard.

(Others are nor calling GPs Orat Tren OT also)