I have a sharp pain if i kneel onto my left knee cap so sharp i yell and fall to one side its ok biking as i tried that today and only a slight ache when walking any ideas i can press the knee cap with my fingers and not cause any pain thanks

You have GKS.

Rickets

nahh! more like BNM.

Housemaids knee.

In all seriousness impossible to diagnose over the net. could be a bruise on the bone, tendon damage, skin infection, housemaids knee, or any one of a dozen other things.

How long has this been happening? Any swelling?

If it doesn't settle in a few days go to your docs

gonorrhoea

It is 100% definitely GKS.

gonorrhoea eats knee-caps.

Sounds like Reactive Rheumatoid Psoriatic Osteoarthritis to me.

Sounds like you've hurt your knee.

Nope – its GKS.

ach you just have the cold ….. mtfu 😉

Ask DFS, they can see into the future.

use some superfeet insoles(other insoles are available)for a bit just to change position. might sort it.

chrondromalacia aka runners knee?

IMHO you should get a sports physio have a look at it.
I've been twice this year,he told me what the problems were, how they came about, what exercises I need to do and that was that. One-stop-shop. £36.
Job done.
I mentioned the second problem with my GP as a side issue to something else some time afterwards and he suggested I see the local physio.
I didn't tell him I already had and it'd really worked out but it was good to hear the same advice.

If all else fails, retire to the settee, with a year's supply of beer and enjoy.

stop kneeling on that drawing pin Pick it up off the floor 😉