Hello,
1. use the Book (opens by pressing TAB key on keyboard), then (while current story quest is selected) press enter > Nishy will turn towards the target position + you will be able to see a big blue beam from that spot.
2. when near the item : crouch (by pressing/holding C key) and Interact (click Left mouse button or tap Enter key)
Feel free to check the walkthru video :
https://www.xvideos.com/video78352043/slavebar_eroge_walkthru_part_2#
Cheers,
~NK