To expand on what An Lon Dubh said:

"fios" needs a fact, a piece of information. "Who he is" is a piece of information, hence "Níl a fhios agam cé hé." "Him" is not a fact, so you can't use "fios".

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A language belongs to its native speakers, and when you speak it, you are a guest in their homes.
If you are not a good guest, you have no right to complain about receiving poor hospitality.

Somebody very close to my heart, go ndéana Dia grásta uirthi, originally from Inis Mór always said:
Tá fhios am é
or
Níl fhios am é
or
Bhfuil fhios ad é?
or
Ní raibh fhios am an fear sin ar chor ar bith
...and things like that for knowing someone or not knowing someone.

I agree that the 'correct' form should be using 'aithne air...' or 'cé hé' - but then again who sticks to the 'rules' when we're having an auld chat....

...oddly enough: 'Níl a fhios agam cé hé' is correct!

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Bí cinnte de go nglacfaidh triúr le gach aistriúchán a thabharfar.
Be sure to get three in agreement with a translation given.

Well, if she used it and she was from Inis Mór, then it's correct. The rules in grammar books aren't as important as what goes on in an auld chat.

(Previous post edited)

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The dialect I use is Cork Irish.
Ar sgáth a chéile a mhairid na daoine, lag agus láidir, uasal is íseal

I am obviously not going to question the lady from Inis Mór, but I regularly hear people whose first language is English make grammar mistakes; it is not a foolproof method.

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I agree with you on that, I wouldn't suggest that just because something appears in conversation that it is correct. The difference with Irish is that, as I'm not a native speaker, I can't confidently say if something is wrong or not, or rather whether it is a nit pick or not. As a non-native speaker my error radar can sometimes be completely off. Stuff I thought was a minor error I've seen native speakers baulk at and things I thought were major errors are apparently just acceptable variants.

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The dialect I use is Cork Irish.
Ar sgáth a chéile a mhairid na daoine, lag agus láidir, uasal is íseal

Tuigim agus aontaím leat.

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Of course there's (the perfectly correct) likes of Tá a fhios agat Seán - 'You know Seán', i.e. what he's like, the way he is.

Cool, I was unaware you could use it like that. Thanks

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Bíonn rudaí maithe mall

What's an error? Is it a mistake when t' old folk of Yorkshire call someone "thee"? And be it wrong when a Hampshire sea dog uses "be" and "is" as distinct verbs? Or when a Welshman says "lovely day is in it? (atá ann)

A lot of things that teachers like to call errors are just dialectal variation, and if dialectal variation is a bad thing, then the subtitles on TG4 all qualify as bad English. I mean, "I'm after doing it"? What sort of grammar is that?

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A language belongs to its native speakers, and when you speak it, you are a guest in their homes.
If you are not a good guest, you have no right to complain about receiving poor hospitality.

My own personal usage -
Tá 'fhíos 'am an fear sin. - I know that man.
Tá aithne 'am ar an bhfear sin. - I know that man. (I personally know him, rather than just recognise him)

You can also say "aithne súl" for knowing somebody but not knowing them personally.

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It is recommended that you always wait for three to agree on a translation.
I speak Connemara Irish, and my input will often reflect that.
I will do an mp3 file on request for short translations.
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