Pronunciation: [wˌɒt ˈɔːl] (IPA) 
The spelling of "what all" may seem confusing to some, as it is not commonly used in standard English. However, it is often used in dialects and colloquial speech. In IPA phonetic transcription, "what all" is pronounced as /wʌt ɔːl/. The first part of the word, "what," is pronounced with the "w" sound followed by a short "uh" sound and a "t" sound. The second part, "all," is pronounced with a long "aw" sound and a soft "l" sound.
The phrase "what all" is an idiom commonly used in some dialects of American English. It originates from the combination of two words: "what" and "all".
"What" can be traced back to Old English "hwæt" and Middle English "what", which mean "anything" or "something". The word "what" is used to introduce an interrogative clause, to ask for information or clarification.
The word "all" can be traced back to Old English "eall", meaning "the whole, everything, everyone". It has its roots in Germanic and Old Norse languages.
When "what" and "all" are combined, the phrase "what all" typically functions as an intensifier. It is used to express emphasis, usually when talking about a variety or range of things.
