を見つけることができた

was able to find

→ を
phrase Uncommon #18,042
was able to find を marks the thing being found; ことができる expresses the ability to do something.
JA: 鍵を見つけることができた。
EN: I was able to find the key.

トムを見つけることができた?

Were you able to find Tom?

とても時間がかかったが、私たちはやっとそれを見つけることができた。

It took a very long time, but we finally managed to find it.

メアリーは探し物を見つけることができた?

Was Mary able to find what she was looking for?

トムは探し物を見つけることができた?

Was Tom able to find what he was looking for?