"Já si tohohle muže pamatuju."

Translation: I remember this man.

[imaldastar]

co to "si" znamená? a proč to je tady?

[AgnusOinas]

"si" is a reflexive pronoun in the dative case (simiarly, "se" is a reflexive pronoun in the accusative). Very broadly, "se" means "oneself" or "each other", while "si" means "to oneself" or "to each other".

Some verbs come with these reflexive pronouns attached and it's best to learn them together just like it's important to learn which case a verb requires (although it's usually accusative).

Thus, this verb is: "pamatovat si + accusative" (pamatovat si koho/co). E.g.: Pamatuju si tě dobře.

There is another (slightly old-fashioned) form of the verb, which you may come across: "pamatovat se na + accusative". E.g.: Pamatuješ se na mě aspoň trochu?

[openminded2]

Why is "mít" one of the English word options in this sentence? It is not English. (d'oh)

[VladaFu]

You mean in the word bank? Duolingo chooses the words automatically and no-one knows how.