What's the difference if there is any?
Look on the front and back of a nickel.
Look at the front and back of a nickel.
Look at is the whole view; look on is presumably in search of a specific part (the date, the engraver's initials, etc).
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Mister MicawberLook at is the whole view; look on is presumably in search of a specific part (the date, the engraver's initials, etc).Perhaps: