How do I know if a topographic layer contains DEM-altitude? ArcMap 10.3
I assume that you mean you have some layer and you want to know whether those data are elevation data of some other data.
If so, find some place on that surface where you know the elevation and check the pixel value there by using the identify button in ArcMap. Or view the data in ArcCatalog, select the description tab, maybe the data creator left some metadata.