Can LR Mobile work with files on a hard drive, or do all files need to be storend in the cloud? I have lots of pictures on a hard drive, and a crashed laptop. How to use the catalogue that was established on a laptop on an ipad?
Which version of Lightroom were you using on the laptop?
If you used the cloud-based Lightroom, then the "catalog" should already be in the cloud and thus should already be synced to Lightroom Mobile on your iPad.
If you used Lightroom Classic, was the catalog sync-enabled? It it wasn't then no, you cannot use the Classic catalog on your iPad. If it was sync-enabled, whatever images you had selected to sync to the cloud would be accessible in Lightroom Mobile on the iPad (but only smart previews, not full res files, as that's all that Classic will upload to the cloud).