自分の能力を

one’s abilities

→ 自分
phrase Rare #43,957
one’s abilities 自分の means “one’s own,” and を marks the abilities as the object of the following verb.
JA: 自分の能力を信じてください。
EN: Believe in your abilities.

若者は自分の能力を正しく評価できないことが多い。

Young people often fail to accurately assess their own abilities.

せいぜい自分の能力を活用しなさい。

Make the most of your abilities.

彼は自分の能力を確信している。

He is confident in his abilities.

彼はよくできない、自分の能力を最大限に利用していないからだ。

He doesn't do very well because he isn't making the most of his abilities.