Does a camel have four knees?

No! Camels (as do all quadruped mammals) have what is called the stifle joint, the equivalent joint to the human knee, in each hindlimb. In the front limb, what is colloquially referred to as the 'knee' in animals such as horses and camels is actually the carpus, the equivalent to the human wrist - not a true knee! So you may say that a camel has two stifle joints (one on each hindlimb) and two 'knees,' (one on each forelimb). Note: the joint down from the stifle (the one which bends in the opposite direction to a human knee) is called the hock or tarsus and is the equivalent of the human ankle.