Meaning
'What's the matter?' or 'what's wrong?' — a run-together contraction of 'what happen'. 'Wam to yuh?' asks what's wrong with you, and, depending on the tone, it can be either concerned ('what's the matter, are you all right?') or confrontational ('what's your problem?'). Clipped right down from 'what happen', it is among the quickest and most common everyday questions, reaching for the cause of a person's trouble or odd behaviour, its exact force — worry or challenge — set entirely by how it is said.
Examples
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Wam? Yuh look worried.
What's wrong? You look worried.
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Wam to yuh today?
What's the matter with you today?
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Wam mek yuh late?
What made you late?
Origin
A heavily contracted form of 'what happen' → 'wa'am' → 'wam'.
How it’s used
Can be caring or confrontational depending on tone. Closely related to 'whappen'.