Trading is more risky because you cannot know everything happening in the market. Skill gambling like poker you know everything before taking a decision and this is less risky. They are both risky and they are not recommended. Usually people who play skill gambling have less losses than the other ones.
How could something that depend on the next card will be less risky? Skill and strategy is just a part of poker but at the end of the day it is the card that is drawn next that decide who will win. It is still not your skill that makes you win rather the card that was drawn next. Unlike trading, if you watch the market and it crashes you have the option to cut loses, in poker, you will never have that option.