In one of the first episodes of season two (I think it was Redemption) Rigsby mentioned Cho was dating someone. Do we just not know who that is yet, of have I missed something?

Cho isn't dating anyone but in one episode he picked up a chick for a prank that Jane set up and in another an old lady was going to give him her daughter of neices number

In an episode during the seconde season, Kimball was revealed to be dating a woman named Elise, someone he was connected with during a case where they had to talk to a Korean woman. The woman pressed Cho to go out with her daughter, and he called her. They talked on the phone, connected, went out. At one point, she was assaulted door people connected to Cho's past. It's generally accepted that the two are still going out, although she hasn't appeared in any episodes since. The episode she gets beat up in is Episode 2.14 : Blood In, Blood Out.