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.