I believe both of them are risky because you will bet your money with something that you are not sure about winning. The only difference is that in gambling if you lose you lose in trading if you are on lose and you do not sell your holdings then you still got the chance to wait for your money to come back to its value.
I still haven't found something known as skill based gambling. If we are needed to compare the address in both of these choices thus simply what I can say is that they are equally risky.
Trading doesn't require practice and the things to improve with time but gambling is all about luck and we could not change the scenario just with the passage of time by polishing our skills. In my opinion only sports betting is something that really offers definite winning if you have been into this since quite a long time.
If anyone is to compare between the risks of these possible methods of earning then obviously I would favor trading over gambling. This is totally a nonsense talk that anything like skill based gambling really exists. Gambling is totally luck thing and trading is somewhat that is experience based and one could excel the method via some practical applications and learning gradually the basic techniques to make a profit out of it.