Can I also say:Kan du gjøre det,eller trenger du hjelp?
Å klare basically means "to manage", if one would be able to successfully complete the task/request. I don't know how "kan gjøre" sounds to a native speaker but it's probably less specific.
"Kan du gjøre det" is somewhat ambiguous but implies a request, like "Could/would you do it?"
"Kan du det?" would be more specific, just like "klarer du det?"