Zzr1100 when riding at very low speed steering is twitchy.

I would flush the steering box really well and re-fill with fresh fluid. If you can get to the lines, it is not too hard to do. There are some additives available for power steering fluid, but the use of them is debatable.

I believe someone driving the tractor has hit a hole or an object hard enough to stop the tractor and literally spun the steering wheel all the way to one side, thereby bending the spindle or the link connecting the steering box to the spindle. Drive the tractor straight on level ground, stop and get off then look standing at a 25 yard distance in front of the machine looking at the symmetry of the front wheels. That will reveal spindle problems.

It may be low on lube and binding when wheels are turned keep them straight and try that - check & change the oil in the transfer case

i would say it is a solenoid or air in the power steering lines but you would have to put a obd2 scanner and see what it says.
if i remember correct bleeding is as simple as removing the power steering cap and turning steering all the way left hold for 5 seconds then right and hold but you will need to look at oil in reservoir and see if it is bubbling while turning and holding. you will need a helper and if it is do this for 5-10 minutes.

you can't, it has to be changed. older steering boxes would turn fairly easy without p/s, but it is not a manual steering box a will be really hard to turn at low speeds, and be hard to keep going straight on the road at high speeds,let alone corners!

Steering neck bearings could be worn. Jack the bike up so that the front wheel is off the ground. Turn steering side to side, if it seems to stick in the middle,(in the riding straight position) then bearings need to be replaced.
Also check swing arm bolt is tight and axle bolts.

raise the truck up and turn the wheels left to right, you most likely have air in the lines.

Sounds like you have air in your steering system. I would start by looking for any leaks on your steering system like hose to fitting crimps, steering pump, etc. Check your steering fluid level to make sure it is full and also look for bubbles on the dip stick. If everything looks good, start the vehicle and turn the wheels all of the way to the left and then to the right. Do this while the vehicle is in park and repeat at least 5 times. This will work out any air in your steering system. If the problem persists then the power steering pump may need to be replaced.

Drive slowly down the middle of a straight road, let the steering wheel go and apply the brakes. If the car wants to turn by itself check your ball joints and shocks. If the car remains straight you may have an irregular wearing tire which causes it wonder at higher speeds.
I hope this helps
Sam