If you have a numberpad on the far right side of the 'board, look at the row of keys above the 7-8-9, or at other rows/columns of keys surrounding the numberpad. The NumLock toggles the numberpad keys between numbers and the other functions/characters shown on them so it's usually close by there.
(I am overly familiar with the NumLock as my job involves a huge amount of data entry which is 90% numbers, hitting the NumLock by accident and turning the numbers "off" in the middle of a long sequence of data I'm typing is one of my little daily frustrations.
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