This is a charade - where two or more words are joined together to make the answer. Look for parts of the clue that can be split into separate components.
Split this into two parts: 'attack on king' gives you the first part (think chess), and 'offence' gives you the second part. The word 'after' tells you the order - put the chess term first, then the word for offence.
Answer: CHECKS IN | This is a charade of CHECK (attack on king in chess) + SIN (offence). Together they make CHECKS IN, meaning registers or arrives.