They can be great apartment dogs. Are they easy to train? Depends on who is doing the training and how well you are diligent in training. Remember, a tired Basenji is a good Basenji... you must work both their body AND mine. Be sure to go to a responsible breeder... and there is loads of information at www.basenji.org
Each basenji is different. Some are easier to train than others. Sometimes it is better to adopt a young adult (especially your first basenji) because you will have a better idea of the problems/behaviors you are getting. As Pat Fragassi mentions, a tired basenji is a good basenji. Do a search on "reasons not to get a basenji" and read as much as you can.
I read somewhere that a basenji goes through life thinking "What's in it for me?" You will forever be trying to out smart the cutest, most intelligent, ornery dog ever.
When I sold puppies, I told people, "I never sell a pup to dumb people." Many still wanted one. Some decided a basenji was not for them - imo, this did not mean they were dumb, it meant they were not baseni folk, and that's ok. I heard one gal, as she was leaving, tell her husband "Why would anybody do this?"
If you decide you might be a basenji person, visit some, and really quiz the owner on what their life is like.
They can do well in a small house, but need walks AND exploration AND interaction with other dogs. Movement is not enough, you need to let them use their mind. When on leash our 2 sisters can sniff all they want, even if it means we do one mile in an hour. They will be tired afterwards.
Trainability: depends on the individual, the age, the human. On YouTube or dedicated fb-pages you can find basenjis showing perfect obedience, even stunningly choreographed doggy dance routines. Will take time and effort and patience. We found that if we treat them along the lines of how you would interact with a 3 year old child, all goes well (most of the times anyway).