My wife has dot on her pinkie toe about 1mm. Not raised. Dark brown. No pain. 2 years+.  concerned?

Melanoma. A new brown spot should always be looked at by your dermatologist. The rate of melanoma is very small in your feet but very bad if it is you and it is not caught early.
Signs of melanoma . Are abcd asymmetry of the lesion. Irregular border color of the lesion..Multiple colors etc diameter greater than 6mm because the lesion is so small, and since you are concerned enough to ask the question, if you came to me, i would remove it. Because, once removed your worrying is over.
Sounds ok so far. A tiny, flat, dark brown spot on the skin, without change over 2 years, sounds like a mole. People usually get more moles as they age. A single small spot can also be a "tattoo", such as from getting poked with a pencil. Mole danger signs include: asymmetry (one side of mole grows faster than other side), irregular border, more than 1 color, diameter more than 6mm, elevated from surface, etc...