This is hard to explain, because we don't have a word like "ever", so if you have more questions, let me know.
"Jamás" and "nunca" are perfect synonyms, so the sentence works with either of them:
El mejor consejo que jamás he recibido. = El mejor consejo que nunca he recibido.
Both phrases mean "the best advice I have ever received."
Why we use "jamás"/"nunca" in this context, is because it's like saying "I have never received such a good advice before this one time".
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