can anyone tell me how to skill my lightning trap assassin?

max LS and its synergies, that's 60 points, then you have some options:
(1) Max Death Sentry & Fire Blast to deal with immunes and have a powerful death sentry that fires lots of times
(2) Put points in dragon talon and be a hybrid trapsin/kicker
(3) Idk what else, you can experiment. It's nice that with the last update, LS only has 2 synergies. Whatever you do, have at least 1 point in death sentry, it's the strongest sin ability by a lot