The British spell it "skilful".
The British spelling of skillful is skillful in a British accent
That is the correct spelling of the adjective "skillful" (talented or competent).
The British speak and use the English language so it would be spelled as skillful.
The adverb form is spelled skillfully, from the adjective skillful.
Skilful (UK spelling) / skillful (US spelling) is not an adverb, no.Skilful/skillful is actually an adjective.The adverb form is Skilfully (UK) / skillfully(US).
The British spelling of supervisor is "supervisor."
Theater becomes Theatre.Honor becomes Honour.Pajamas becomes Pyjamas.Skillful becomes Skilful.
That is the correct spelling of "talented."
The British spelling is "squash" and the American spelling is also "squash." Both countries use the same spelling for this word.
The word is spelt as you have in the question. As it happens, there is no difference between the American spelling and British spelling of the words.
The British English spelling of marvelous (astonishing; wonderful) is marvellous.
British spelling: meagre