Your raster TIFF should go in the Points/Lines port, the points you want to get Z value for should go into the Drape Features and then the Surface Tolerance parameter is one of those mysterious things that even after reading the Help I’m not exactly sure what it does. If you enter 0 it will simply not filter out any points so let’s go with that for now.
It is of course important that your raster and points are in the same coordinate system, so you need to reproject if they’re not.