where I can get some data about the stake difficulty?
The network aims to stake 1 CLAM per minute. Some 600k CLAMs are trying to stake. The difficulty will be roughly set such that the 1-per-minute goal is reached.
Running "getinfo" in the CLAM console will tell you the current difficulty.
dooglus told me the reward is around 2% per day of the deposited amount of clams
No, I told you 0.2%:
One more question if you are so kind to help me if you know, which one is the most ptofitable POS coin?
Right. You currently get to stake about 0.2% per day of your CLAM balance.
, but I didnt get if this % is fixed or if I deposit let's say 1000 calms I'll get 0,4% and so on?
It's not fixed, since the network continues to try to stake 1 CLAM per minute as the number of CLAMs attempting to stake tends to increase. That results in the rate of return dropping over time. And staking is random. You're running a hash function every 16 seconds per output in your wallet and hoping for the output to be less than some target based on the current difficulty. The rate of return doesn't depend on the amount of CLAM you hold, but the variance decreases the more you hold. It's like buying a thousand lottery tickets compared to buying just one. The expected value of each ticket remains the same, but you approach the expected return with lower variance the more tickets you buy.