How do you find the acceleration due to gravity on Pluto?

You can look it up. If you mean, how do scientists figure it out, they will have to calculate, or estimate, Pluto's mass, and its diameter. Once these are known, the acceleration by gravity can be calculated very accurately. The real challenge lies in finding out those two things.

The diameter can be observed in high-resolution telescopes. With interferometry, a very accurate image can be obtained.

The mass can be calculated by its gravitational effect on other objects, includings its three moons. Perhaps New Horizons will be able to measure the mass more accurately, once it arrives.