Hi, I would use "that" instead of "where" or "which". You also don't need the comma after "inventions" but one is needed after "info". The phrase, "an unlimited source of info" is a nonessential appositive clause. It is set off by commas, and adds detail, but It can be removed without changing the meaning of the sentence. :-)
I'm not sure in what context the phrase is originating from but here's my 2 cents. "Many people affirm that one of the inventions is the internet, an unlimited source of info, that you can access on almost any electronic device." The clause that comes after "that" adds meaning to your sentence; it wouldn't be the same without those details. "Which" would be used if you can leave out the clause that comes after it without changing the meaning of the sentence.