My SGUnited Traineeship is ending soon. Should I apply for another traineeship?

Firstly, instead of continuing to look for traineeships, is there an option of converting into a full time employee with your company?

Also, why do you feel unconfident in your skills from your traineeships? From what I've seen of my trainees in the company, they're given a good slice of work to do and I warrant that what they've done would have been a respectable amount even when compared to an entry-level position in another company.

If you feel like you've learnt and have a clearer picture of the industry, I suggest just apply for a full time position. Unless you've been doing nothing at your traineeship, having some doubts about your skills is perfectly normal! You mentioned that you are unsure about your interests, so ask yourself, did you enjoy the role you were in, if you didn't hate it and you're "okay" with it, I would suggest to just apply for the FT role.

As a full timer, you will have additional responsibilities, which also means that you will be able to learn and try more. This will allow you to experience the role more acutely and from there you can figure out if you would like to continue in it. This will also look a lot better than just being a trainee repeatedly.