You can see how many subtitles you've written so on Viki by going to your profile page.
You can go to your profile page by clicking on the down arrow next to your profile picture at the top right of any Viki page, and choosing "Profile".
On your profile page, you can see the total number of subtitles that you've written on the right hand side of your profile picture.
If you'd like to see the exact subtitle you've written, go to your "Project Contributions" tab. Then select "Subtitles" from the drop-down on the right. Each page will show the 15 most recent subtitles you've written.