It is spoken language. I should have mentioned it was subtitles.

Subtitles are often mis-spelled, or spell the word as it’s pronounced or mis-heard (so if it’s mis-pronounced it’s mis-spelled, or if it’s pronounced colloquially rather than formally).

Je ne sais pu quoi faire

It should be spelled, Je ne sais plus quoi faire i.e. “I no longer know what to do” or “I don’t know what to do anymore”.

je ne sais pu c’est de quel côté c’est ici ou ici

“I don’t know any more — which side is it — is it [or ‘it is’] here or here”

Ok so its not a mistake at all in speech, its perfectly fine and can be exchanged for ‘plus’ with the same meaning. Ok I get it, thanks.

There are several versions of French — see Registres de langue en français for example — and ideally you’ll use the right one for the [social] context.

(Plus there’s local patois).

People go to school to learn the courant and soutenu (correct and formal) versions: in which pu is une faute, and plus is correct.

A benefit of school French is that it’s relatively clear and doesn’t result in questions like this one … it’s also maybe the most “polite”, and may be expected in a business context, etc.

I’m not sure what the benefit of informal French is — perhaps it’s to mark you as an insider of a social in-group, friends who can take liberties (with the language) with each other.

Because I’ve been to school, when I listen to the radio I can understand every word they say on France Culture, for example … and I understand almost nothing they say (e.g. I miss at least one word per sentence) on a youth-oriented music station when the DJs are chatting and joking with each other.