I tried a different Sim in a different save. If you have two Sims talking to each other, Get To Know only seems to work when it is the last interaction in the queue. Even with just one Get To Know, I didn't learn a trait if I had any other interaction after it. This makes it almost useless, since I almost always use a full queue for conversations.
I also tried one group conversation with two Get To Knows in the queue and it functioned normally, allowing my Sim to learn two traits from the same Sim. I've only made one test though.