What Does This Mean In Arabic: "Neylou Walla"?

Well, as an arabic speaker, I actually couldn't understand what exactly you mean, but I think you meant something pronounced "ney yalo wallah".

If so, it means something like "he deserves it".

Its a common Lebanese word to say when something positive happens to your friend or someone you like (as a third party)

Sorry if that was not helpful,
If it wasn't what you look for, try to write it again but in clearer letters, even if you split it to many words
(Excuse me for my bad English, I'm still learning)

Ciao

The walla part here kind of means 'by God' والله used to emphasise. So he 'truly' deserved it, or 'he deserved it, I swear by God' (though the English use is more dramatic than the Arabic). It's used a lot: Walla ma fi - 'really, there is none', walla hilu - 'that's nice, really'.

Perhaps neylou is a colloquialisation of نال له (nal lehu). Literally 'he truly got it', but meaning I think, in agreement with the guest above, 'he deserved it'.