Since this word has okurigana (hiragana attached to the kanji) you know that it's probably going to be the kun'yomi reading, which you didn't learn with the kanji. Here's a mnemonic to help you:
You finally finished your school project. "Oh, A!" (おえ) you say to yourself, as though you can grade your own project.
I want to finish work and leave the office by five.
As soon as the princess finished the cake, she had some tea.
Most fish spend their entire life in water.