I want to series the solar panel up and have voltage regulator that can regulate it.
You're not going to be using the LM317 as a voltage regulator in this case. It will solely act as a current regulator, also known as a constant current source. (CCS).
How does the lm317t react when my solar panel hit shade and current goes under 200mah.
I would expect it to simply pass the current it gets as input in this condition, up to the point where the regulator doesn't get enough current to operate, which will happen somewhere under 10 mA. At that point, you'll get a large voltage drop across the LM317-as-CCS, and current through the regulator will drop off sharply. (There may be some residual leakage.)
I hesitate to guess whether this voltage drop will present as a cliff or a ramp.
It's not hard to test it and find out, though, and you have the equipment, which I do not. (I have LM317s on hand, but no bare solar panels.)
What voltage should I put on my voltage regulator that i will connect to lm317t
You shouldn't need a voltage regulator.
Think of the LM317 in this circuit as a rubber band between the voltage source and the sink. That is, between the series-connected solar cells and the NiMH battery. When the source voltage rises due to higher insolation, the voltage drop across the LM317 will increase accordingly, soaking up the difference between the battery voltage and the solar array voltage. As the battery charges, its terminal voltage will increase, decreasing the voltage across the LM317.
What current should be held constant to charge 7.2v 2000mah nimh?
You should set the LM317 for 200 mA or less, to avoid exceeding an 0.1C charge rate, which is the fastest you should charge a NiMH battery if you do not include safe methods of early charge termination, such as -ΔV detection and overtemp detection.