Learn Portuguese (Portugal): Concentras-te no teu mestrado? - Do you concentrate on your master's degree?

The verb concentrar-se always requires the preposition em to show what you are concentrating on. In this sentence, em merges with the masculine definite article o to become no.

Why is there a -te attached to the verb concentras?

In Portuguese, the verb to concentrate is reflexive: concentrar-se. You literally express that you concentrate yourself. Because the verb is conjugated for the informal you (tu), the matching reflexive pronoun is te.

If no is a contraction of em plus o, why do we need the article o before teu?

In European Portuguese, possessives like teu almost always take a definite article before them. The preposition em combines with this article o to form no, so you are literally saying on the your master's degree.

How would I ask this same question formally?

To speak formally, you change the verb to the você form and use the reflexive pronoun se. The possessive also changes to seu, making the full sentence: Concentra-se no seu mestrado?