how do translate the last name Wong in Mandarin?

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There are many dialects in "Chinese" language, including the 'Mandarin" that you want to search for, and many others like "Cantonese", "Taiwanese", "Hakka", "shanghainese", "Hunanese", "Sichuanese".......

the last name "Wong" is most probably use in "Cantonese", it refers two Chinese character of "黃" or "王" , both of them are last name.
So which one is what you asking for?

in "Mandarin" >
"黃" is "Huang" (for pinyin) and "ㄏㄨㄤˊ" (for zhuyin)
"王" is "Wang" (for pinyin) and " ㄨㄤˋ " (for zhuyin)

remark : "zhuyin" is the one previously using in China before change it to "pinyin" ; and it remain & still usually used in Taiwan
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Could be 黃 [yellow] (Pinyin: Huang) or 王 [king](Pinyin: Wang)

Either could be represented in Cantonese or other dialects as Wong.

黃

i admire Jalen Wang out of your record, yet indexed here are another innovations: Collin Wang Connor Wang Peter Wang Phillip Wang Hector Wang Alexander Wang Matthew Wang Thomas Wang Steven Wang Cory Wang Anthony Wang Marcus Wang Mackenzie Wang Michael Wang Toby Wang Jarod Wang Jacob Wang Brian Wang Jack Wang Edward Wang Jermaine Wang Jeremiah Wang Casey Wang

王...