On the Work Order, you can use Add Checklists action. It will open a window where you can specify which checklists you want to add.
You can use the same action on the work order resource line to add a checklist to the selected line.
For work order and posted work order you can do this also directly from the page with all checklists on the selected record (the list can be opened directly from the specific record with the Checklists action) - remember that on the posted work order there is additional action with the same name that is showing all checklists filled in on the work order. This way you can add only checklists to the document, not to its resource lines.