The Add Points --- > Stairs and Add Points --- > Topography command will not allow selection of stairs or topography in linked models. This is due to limitations of the Revit API. You can, however, project points onto stairs or topography in linked models, using the Add Points ---> Projected command.
Step 1 ---> Define the Projection Region
Add a Filled Region, above the stair case, on the top level of the stairs.
Step 2 ---> Add Projected Points
Select the foot print region created in step 1.
Step 3 ---> Set Target Category to Stairs
Step 4 ---> Check "Multiple Intersections Enabled" as needed.
This allows points to be projected onto stairs spanning multiple levels.