Learn Swedish: Jag vet att spårvagnen inte kommer klockan sex prick. - I know that the tram does not come at exactly six o'clock.

Because it is inside a subordinate clause. The word att (that) starts this clause. In Swedish, subordinate clauses follow a special word order where sentence adverbs like inte come before the verb. A common memory trick for this is the BIFF rule: in a subordinate clause, inte comes before the verb.

What does prick mean when talking about time?

It translates to 'sharp' or 'exactly'. The word prick literally means 'dot', but adding it after a time, like klockan sex prick, means 'six o'clock on the dot' or 'six o'clock sharp'.

Why isn't there a word for 'at' before klockan sex?

In English, you say that something happens 'at' a certain time, but Swedish usually drops the preposition for exact clock times. You just say klockan sex (the clock six) instead of trying to translate 'at' with a word like på or i.