I'm fairly certain I can do the job.

我有相当把握能干这项工作。

《牛津词典》

I can do the job myself.

我可以自己完成这项工作。

youdao

I can do the job alone.

我可以一个人做这份工作。

youdao

If we had good boards, I think they could certainly do a better job of that than the government can."

VOA: special.2009.10.30

You are doing a great work. Keep up the good job because I know you can do it.

你做得真棒！再接再厉哦，相信你能行的！

How long课堂 - SpeakingMax英语口语达人

But I got laid off. So I'm waiting for Barack to do something about the economy so I can go back to my regular job."

VOA: standard.2010.07.20

Sometimes, that "I can do the job" confidence is so intense that investors run the other way.

FORBES: The Secret To Wooing Investors

If they just email me the job specs, I can easily do the job.

FORBES: Working From Home: The End Of An Era?

The one thing that I think helps me handle the stress is if I feel like, at the end of the day, I've done the best possible job I can do, even if not everything has worked out exactly the way I planned it, then I feel okay.

WHITEHOUSE: President Obama Unveils his Budget to Win the Future