Count the liberties
When two enemy groups both lack two eyes and share liberties, they fight a capturing race (semeai): whichever fills the other's last liberty first wins. To read it, count each side's outside liberties, the shared liberties, and the order of vital moves. If you have more total liberties and the move, you win; if not, look for a tesuji (a snapback, a big-eye killer, a liberty-throw-in) to swing the count.