Questions & Answers about Куда ты идёшь после работы?
Why is куда used here instead of где?
Because куда asks about destination: to where?
- Куда ты идёшь? = Where are you going?
- Где ты идёшь? would mean something like Where are you walking? or In what place are you going?, which is a different idea.
A useful contrast:
- где = where, in what place
- куда = where to
- откуда = where from
Since this sentence is about movement toward a destination, куда is the correct question word.
What form is идёшь?
Идёшь is the 2nd person singular present tense form of идти.
So it matches ты:
- я иду = I am going
- ты идёшь = you are going
- он / она идёт = he / she is going
The ending -ёшь tells you it goes with ты.
Why is the verb идти, and not ходить?