Learn Italian: Sai se gli è piaciuto il discorso? - Do you know if he liked the speech?

The verb piacere (to like) works backwards compared to English. It literally means 'to be pleasing to'. In the past tense, it always uses essere (to be) as its helping verb, never avere (to have).

Why does piaciuto end in '-o' here?

In sentences with piacere, the thing being liked is the actual grammatical subject. Here, the subject is il discorso (the speech), which is a masculine singular noun. The past participle (piaciuto) must match it. If he liked a feminine word like the song (la canzone), it would be è piaciuta.

How does gli translate to 'he' in this sentence?

Since piacere means 'to be pleasing to', you use an indirect object pronoun to say who is receiving the pleasure. Gli means 'to him'. So, gli è piaciuto il discorso literally translates to 'the speech was pleasing to him'.

Why do we use sai for 'do you know' instead of conosci?

In Italian, you use sapere (here conjugated as sai) when you know a fact, a piece of information, or before a connecting word like se (if). You only use conoscere when you mean you are familiar with a person, place, or thing.