The Add Points --- > Stairs and Add Points --- > Topography command will not allow selection of stairs or topography in linked models. You can, however, project points onto stairs or topography in linked models, using the Add Points ---> Projected command.
Note: To project points to elements in linked models, the linked model needs to have at least one 3D view where the elements are visible.
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.