What do you mean by "find the functions"? They are pretty much right there aren't they?
As for the domains, both of those are square roots. Which numbers can you take the square root of which can you not? I assume we are talking about real numbers.
I know how to find the domains of the individual functions. I don't know how to combine the radicals and find the domain of that resulting function.
To answer your question, the domain for f is x is less than or equal to 5 because any value for x greater than 5 would put a negative under the radical. For the same reason, the domain for g would be x is all real numbers excluding 2 and -2