We have shelf notes in Primo for most of the Course Reserves books. If you need to add a public note, this is what you do:
1) Search PHYSICAL ITEMS: Scan item barcode
2) From the three dots: select ITEM
3) Click the NOTES TAB
4) Enter the shelf note in PUBLIC NOTE field. It appears in the system immediately.
You should also be able to do this from ALL TITLES, but it might be a few more steps.