first time

my first plant and it was root bound when repotting how much stalk should be under dirt

You can bury as much as you want if you have a deep pot to go into, but leave some room between the dirt and the lowest set of branches.

If you mean you are going to translplant a root bound plant than the answer is you can bury the stalk all the way to one inch below the first set of leaves and be ok. Make sure you prepare you new pot, dig a hole so your old pot slides in and out like a piece of ice in a tray. Than dry our your existing plant, tap the sides of the pot, lift it out and just slide it in the new hole. than burry with new soil like you want up the stalk and water. If you do it this way you will have zero stress and the roots will just begin to go and grow.

Good luck