Questions & Answers about Učitel jí dá odpověď.
Jí is a pronoun in the dative case, feminine singular.
Here it means to her.
So the whole sentence is essentially: The teacher will give an answer to her.
Czech distinguishes cases by both form and vowel length:
- ji = accusative (direct object) of ona – her (as the thing directly affected)
- jí = dative (indirect object) of ona – to her / for her
In this sentence, she is the indirect object (the person who receives something), so Czech uses the dative: jí.
If she were the direct object, you would use ji instead, e.g. Vidím ji (I see her).