Learn Italian: Il pettegolo ha confermato vagamente la soffiata. - The gossiper vaguely confirmed the tip-off.

Here, pettegolo is a noun meaning "the gossiper" (the person). If you want to talk about a rumor or a piece of gossip, you would use the noun pettegolezzo. Pettegolo can also be used as an adjective, as in un uomo pettegolo (a gossipy man).

How does the word soffiata come to mean "tip-off"?

It comes from the verb soffiare, which means "to blow". In colloquial Italian, a soffiata implies a secret being whispered or "blown" into someone's ear, making it the perfect word for a tip-off, leak, or insider information.

Could the adverb vagamente be placed at the very end of the sentence?

While you can place it at the end for special emphasis, the most natural position for an adverb of manner (ending in -mente) is immediately after the verb it modifies. In compound tenses like the passato prossimo, it goes directly after the past participle (confermato).

Since this lesson focuses on limitative clauses, how would I add "as far as I know" to this sentence?

You can use Per quanto ne so (with the indicative) or Per quanto io sappia (with the subjunctive for a slightly more formal, doubtful tone). Placed at the start of the sentence, it perfectly restricts the certainty of the rumor: Per quanto io sappia, il pettegolo ha confermato vagamente la soffiata.