Learn Turkish: Bu sorun çok küçük. - This problem is very small.

In Turkish, there is no separate word for 'is' in the present tense. When describing a third person or thing like sorun, you simply place the adjective at the end of the sentence. The phrase çok küçük acts as the whole action, meaning 'is very small'.

Could I say 'Bu çok küçük sorun' instead?

That would change the meaning to 'This very small problem' rather than a full sentence. To make a complete sentence stating what the problem IS, the describing part çok küçük must come after the subject bu sorun.

Is sorun related to the word soru (question)?

They look very similar and share the same root, but they mean different things. You will see soru used for a 'question' you ask, while sorun is used for a 'problem' or 'issue' you need to solve.