Learn French: Dans le cours de philosophie, on parle toujours de soi. - In philosophy class, one always talks about oneself.

Soi translates to "oneself." It is a stressed pronoun used only when referring back to an unspecified person or a general subject like on (one), chacun (everyone), or personne (no one). If the subject were a specific person, like il (he), you would use lui instead.

Since on usually means "we" in spoken French, could this sentence mean "we always talk about ourselves"?

No, because of the word soi. When on is used to mean "we," the corresponding stressed pronoun is nous (on parle toujours de nous). The use of soi proves that on is being used in its general sense here, meaning "one" or "people."

Why is toujours placed after parle instead of before it like in English?

In French, you generally cannot separate the subject (on) and the verb (parle). Short, common adverbs like toujours (always) must be placed immediately after the conjugated verb. So, "one always talks" becomes on parle toujours.

Why does the sentence use Dans le cours instead of just En cours?