Learn French: Évidemment, je l'ignore. - Obviously, I am unaware of it.

This is the neuter pronoun le (elided to l' because the verb starts with a vowel). Instead of replacing a specific masculine noun, the neuter le replaces an entire idea, fact, or clause that was just mentioned. It gives the meaning 'I am unaware of it' or 'I don't know that fact.'

Doesn't ignorer mean 'to ignore'?

It is a classic false friend! While it can sometimes mean deliberately ignoring someone in modern French, its primary and most common meaning is simply 'to not know' or 'to be unaware of.' So Je l'ignore translates to 'I don't know it' rather than 'I am ignoring it.'

If the translation says 'I am unaware', why isn't there a ne ... pas in the French sentence?

The verb ignorer carries the idea of 'not knowing' all by itself. If you added ne ... pas, you would be creating a double negative. Je ne l'ignore pas would actually mean 'I am not unaware of it' (which is a formal way of saying you actually do know it!).

Why does évidemment end in -emment instead of -ement?

Most French adverbs are formed by adding -ment to the feminine form of an adjective. However, adjectives that end in -ent (like évident) drop the -nt and add -mment instead. Note that this ending is pronounced with an 'ah' sound, not an 'e' sound.