Is the process kno3 dissolving in water spontaneous at all temperatures studied?

No

Explanation:

the dissolution of potassium nitrate in water is an endothermic process because hydration energy does overcome the lattice energy and hence it is not spontaneous at all temperature.

Hydration energy: it is a energy released when gaseous ion is dissolve in the water during dissolution it releases.

lattice energy: the energy which is released when one of ionic compound is formed from their gaseous ion is called lattice energy.

thats why to break it we should give minimum this much energy