Meaning
'What's wrong with you?' or 'what's the matter with you?' — asked of someone acting oddly, foolishly, or out of sorts. Depending on the tone, 'wah do yuh?' ranges from genuine, caring concern for a person who seems unwell or troubled, to a sharp rebuke at someone behaving strangely or badly ('wah do yuh, man?'). A very common everyday question, it reaches for the cause of a person's off behaviour, whether in worry or in exasperation.
Examples
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Wah do yuh? Yuh a cry fi wah?
What's wrong with you? What are you crying about?
Concerned tone, asking after distress.
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Wah do yuh, man? Yuh caan drive so!
What's the matter with you, man? You can't drive like that!
Scolding tone, reacting to bad behaviour.
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Mi nuh know wah do yuh dis morning.
I don't know what's gotten into you this morning.
Used as an embedded clause, not a direct question.
Origin
From 'wah' (English 'what') + 'do' (English) + 'yuh' (English 'you'); the construction parallels 'what ails you'.
How it’s used
Tone is everything: softly it shows care, sharply it accuses. Directed at a stranger in anger it can escalate a confrontation.