a personal trainer at your gym has no more knowledge than any other person at the gym.. the only difference is they took some test that any retard can pass
as far as a training partner i do not see any upside to it on a regular basis. it can actually backfire even if they 'push you'.. a great way for you to overtrain or get injured. every person is different and this is an individual hobby so i don't recommend training in a group or with a partner regularly. spotting each other here and there is fine, but doing every lift together and such makes no sense cause we all have different goals and abilities