This is a charade - two separate words or phrases are joined together to form the answer.
Break this into two parts: find a word meaning 'wonderful' and combine it with 'piece of writing'. The question mark after 'power' suggests the definition is cryptic or punning.
Answer: SUPERSCRIPT | SUPER (wonderful) + SCRIPT (piece of writing). A superscript shows mathematical power, like the ² in 10².