how can a person master martial arts without trainer?

 you can learn martial arts with a friend. A sparring partner is the most important aspect of training. An instructor is pretty important too, but not as important as a sparring partner

is siaolin best than karate?

Kung Fu therefore is more useful in situations where you might be grappling with your target, while Karate is a more offensive martial art. In a general sense, Karate can be used more efficiently to harm an opponent while Kung Fu can be used to stop an opponent.

Answer:

he/she must be trained he will not learned if he never learned anything