Do you mean the steering knuckle? If so, the cv splines may be seized to the knuckle. In this case you may have to soak the splines with a good penetrating fluid and really give it a good hit with a hammer and a drift. If the axle is junk then you can hit it without the drift for more force but this will damage the threads.
If that doesn't work, you can try heating it, but this may ruin your wheel bearing that is located around the splines.
You may also use a puller or a bench press as a last resort as well.