Not sure how many screens you have or your config but it could be displayed as part of a DMD image (best if you have a virtual DMD that's not 4:1 display ratio), or as a Topper image.
But the easiest way would be if you have a 5inch or similar 'apron' screen (doesn't have to be located on the apron, it could be located anywhere), in PinballX the designated apron screen will display whatever image you have in instruction media for a table all the time. If you use the instructions menu in PinballX regularly and don't rely on the instructions on the table itself that might not be an option though. (some links in my post here https://forums.gameex.com/forums/topic/25368-pincab-scutters-pincab/ for the apron screen type i use)
See Mikes link for the VB plugin template, or @jejegameex's version if C# is your thing - https://forums.gameex.com/forums/files/file/2541-pinballx-plugin-snap-in-template-c-net-framework-20/
You might find some useful stuff in VB the plugins i've done, see https://ftpbrowse.gameex.com/-PinballX-/Other Uploads/scutters/Plugins/
If you do go that way and get stuck then post back!.