Learn Turkish: Yolcu ülkesine dönüyor. - The passenger is returning to his country.

The word ülkesine translates to "to his country". The root is ülke (country). To say "his country", we add the 3rd person possessive suffix -si to make ülkesi. Next, we need the "to" direction suffix (dative case) -e. When adding any case suffix to a 3rd person possessive, Turkish requires the special buffer letter -n-, rather than the usual -y-. So it becomes ülke + si + n + e.

Why is there no Turkish word for "his" in this sentence?

In Turkish, possessive words like onun (his/her/its) are often dropped. The suffix -si in ülkesine already proves that the country belongs to a third person (the passenger). You could say Yolcu onun ülkesine dönüyor, but dropping onun sounds much more natural.

Why does the verb dönüyor use the vowel ü before -yor?

The verb root is dön- (to return). Because it ends in a consonant, we need a helper vowel to connect it to the present continuous suffix -yor. Following the rules of 4-way vowel harmony, the vowel ö in dön- requires the helper vowel ü, giving us dönüyor.

Is yolcu related to the word yol (road)?

Yes! Yol means "road" or "way". The suffix -cu (which can change to -cı, -cü, etc., depending on vowel harmony) is used to create a noun describing a person associated with that thing. So, yol plus -cu creates yolcu, meaning a traveler or passenger.