Are cardamom husks edible?
The entire seed pod is edible. With a coffee grinder, you may not be able to reduce the husks to powder (that’s more of a job for a burr grinder), which may affect the mouth feel of the final dish slightly but should be fine. The cardamom taste comes from the seeds, so you can remove the husks if you want, but I wouldn’t bother.
If you do decide to remove the husks, the easiest approach is to squeeze each pod along its longest axis (so, trying to make it shorter). This will tear the sides of the pod and expose the seeds. For fresh cardamom they may be in the form of a slightly sticky cluster. Either push the seeds out with your fingers, or scrape them out with the tip of a knife.