Went for a ride several days ago on the K100 and heard a knock from the front end when braking and turning into a parking lot. I thought the horns were hitting the fairing. I moved the horns and still have the noise. I can duplicate noise if I sit on the bike and hold the front brake and compress the front forks. It sounds like it's coming from one of the forks. Any ideas on what to look for???

How long since the fork oil was changed? Any leaks at the drain bolts?
Type of oil used?
Check the tightness of all of the bolts for the front end (mudguard, triple clamps, brake caliper mounting bolts, axle pinch bolts etc).

The only thing that comes to mind is the allen bolt which is up the center of the leg from the bottom may be lose but I would expect to have some oil evident as well. Would pay to check that (you will need to remove the front axle to get at it) and renew the oil as I am thinking worn out oil that is as thin as water could let it rebound a lot quicker than desired and cause a knock at the top out.
Another thought is with the axle out check the wheel bearings.

Oil just changed,muddy water came out,atf back in,no leaks,I have checked all mounting bolts but have not checked wheel bearings although when I installed the front tire they turned smoothly. I'm thinking internal in the fork. I will advise. I will say that the forks compress very easily, when I jack the front wheel off the ground I can compress the forks about 2 inches just by lifting up on the wheel then it starts to get firmer. Normal?

That sounds like the springs have had it. Try to get a known good spring and compare but I think you will find a shagged spring or two.

better have a look at the schematics chris ....theres a few o rings in the lower part of the legs .......and as k_freak suggested ...maybe the springs have settled (for want of a better word ) .

there are also shims in the top end to take up slack between the spring , spacer and circlip holding them all in place ...maybe a check could be conducted .

raise the front wheel (bike on centre stand and jack up under the sump so the front wheel lifts off deck) ...undo the caps at the top and see if there is slack (space ) between the shims and circlip ?

maybe a set of "progressive" springs might be a good option for replacement, there may be many other options, just one that came to mind .

I'll check the springs today and let you guys know whats going on.