Can I show task ID on closed cards?

Yes - to make this possible, go to board Settings - Card Template and enable the External ID field. Can I show task ID on closed cards?

You can select a few additional options:

for the ID to be visible on fronts of cards or not,
to have the ID editable or not,
for it to be generated automatically for each new task or not,
and for the numbers to be sequential (to start from “1”) or not, in which case the ID will be a random multiple digit number, the same in fact as a task’s internal ID - as seen in an open task’s URL.

Another way to show the ID - or any other information from within the card - in closed card view, is to use the Task Summary power-up. You’ve got full control over what data your cards are showing.

Kanban Tool is a visual management solution that helps companies visualize workflow, track project progress, and analyze and significantly improve business processes. Kanban Tool provides powerful online Kanban boards with seamless time tracking and insightful analytics. Our Kanban software works perfectly in any business process and is designed for teams that want to visualize work on a Kanban board.