"Est-ce que tu te souviens de ce chien ?"
Translation:Do you remember this dog?
In another similar question one lesson back, it was considered redundant to "Est-ce que" at the beginning of a pronominal question and it was marked incorrect when I used it as a French translation of the English. Here it is actually used in the French sentence we have to translate English! Lol
"Est-ce que" is used before a statement to turn it into a question. Perhaps, as Summerstor5 points out, what you saw was actually already a question (i.e., using inversion). In that case you do not use "est-ce que" before something that is already constructed as a question.