If you check the documentation (browse on from the help) you will see this:
load topo
Create a raster reference object associated with the topo raster grid.
R = georefcells(topolatlim,topolonlim,size(topo))
and a couple of lines further down:
Define the points you want to interpolate using latitude and longitude.
mylats = [-40 -20 20 40];
mylons = [ 42 54 38 62];
Interpolate the values at the defined points.
Vinterpolated = geointerp(topo,R,mylats,mylons)
There's also a live-script illustrating the workings.
HTH