Copying holding clearances involves recording revised routing, holding pattern specifics, an altitude clearance, and an expect further clearance time. It’s often the most complex ATC clearance issued.
On top of all that, the clearance is random. ATC may ask you to hold anywhere on your cleared route, or the controller may direct you to hold at point that is not on your route.
If that weren’t bad enough, holding clearances often occur as a surprise. You were expecting to continue to your destination when ATC suddenly stops you in your tracks. This may occur for any number of reasons.
Here’s an article with tips and techniques for copying holding clearances.
If you would like hands-on practice copying holding clearances as well as most other types of clearances issued by ATC, check out Clearance Magic.