Wǒ huì jǐnkuài.

我会尽快。

As soon as I can.

Notes:

我(wǒ): I

会(huì): will

尽快(jǐnkuài): as soon as possible

Example:

A: 这个项目什么时候可以完成？

    Zhè ɡe xiànɡmù shénme shíhou kéyǐ wánchénɡ? 

    When will you finish this project?

B: 我会尽快。

    Wǒ huì jǐnkuài. 

    I will finish it as soon as I can.