What would the pressure and temperature of gas be, right above Jupiter's gas/liquid boundary?
Technically there isn't really a gas-liquid boundary because temperatures are well above the critical point of hydrogen (33K and about 18bar). It's a supercritical fluid. There are important changes at various depths though including the bottom of the circulating winds, the transition to metallic hydrogen and (it now appears) an increasing density of dissolved/suspended heavier elements making up a somewhat diffuse core. There is lots of "pre-Juno" information easily accessible, including temperature and pressure at the transition to metallic hydrogen (10000K and 20GPa). This source gives a pressure of 100kBar at the bottom of the circulating winds layer (about 10 GPa), but I can't find a temperature.

I just found this very interesting diagram: from these lecture notes which shows how the expected temperatures and pressures inside all the giant planets relate the various phases of hydrogen. Notice how all of them except Jupiter do cross the short curved black line at the left, so that they do have a gas-liquid boundary at pressures of a few atmospheres and temperatures of a few tens of Kelvin