maxlag will have physical units of length–whatever your data’s coordinates are expressed in. (This will “work” if your data are in lon/lat coordinates, but you should really project them to UTM or whatever, since one degree of longitude represents a varying physical distance as you move from the equator to the pole.)
nlags does not have units–it’s just the number of bins the variogram point cloud gets averaged into (i.e., the number of points/bars in the figure here).