Learn Turkish: Bildiğim kadarıyla, kıyafet kodu hakkında uyarılan taşeron geç kalacak. - As far as I know, the subcontractor warned about the dress code will be late.

It breaks down into uyar- (to warn) + -ıl (the passive suffix) + -an (the subject relative participle). Without the passive suffix, uyaran taşeron would mean "the subcontractor who warns". Adding -ıl makes it passive, so uyarılan taşeron becomes "the subcontractor who is/was warned".

Does uyarılan indicate when the warning happened?

The -An participle doesn't have a strict tense on its own; it can refer to the present or the past depending on context. Here, logic and the future tense of the main verb (geç kalacak) tell us the warning has already happened, which is why we translate it as "the subcontractor who was warned".

Can you break down the phrase bildiğim kadarıyla?

This is a very common set phrase meaning "as far as I know". It combines bildiğim (what I know — using the -dik object participle + the 1st person possessive suffix) with kadarıyla (with the extent/amount of). Literally, it translates to "with the extent of what I know". You can swap the verb to make similar phrases, like gördüğüm kadarıyla (as far as I can see).

Why is it kıyafet kodu instead of just kıyafet kod?