Like its already been said - "knock knees" is desirable.

In my experience, many new cyclists tend to ride with their knees out - and so do many older cyclists.

That was certainly me, with one knee pointing more out than the other.

Getting my knees both pointing forward alleviated knee discomfort.

Getting my knees in the habit of pointing in to the frame has "disappeared" my knee pain and of course in a race situation, you become more aero.

Having knees pointed out, or even straight ahead creates a "bucket" which "catches" wind and slows you...

The most important thing is your comfort though... find the best way for you to ride and stick with it.