I identified how to export a catalog from the HD attached to the laptop. I now have the catalog as a separate project and it's ready for import to the desktop. I can't figure out how to combine as oppose to have it as a stand alone catalog.
I utilized the <Import from Another Catalog> and the images are copying over. While clicking next, I noticed that in addition to the images, the Ircat was also going to be copied over. I only have one catalog for my entire LR (therefore only one Ircat). The Ircat is maintained on a separate hard drive than the images. As I watch the files copy over, I don't see an Ircat file appear with the photos.
1) Is LR smart enough to automatically combine the Ircat (from the import) with the existing Ircat file on my desktop computer?
Once this is successfully completed, I'll update the post so the next person has step-by-step instructions.
From the external HD via a laptop:
1) <File>, Export as Catalog
2) Provide a name and location to save the catalog
3) Check "Export Negative Files"
4) Wait while the catalog is created. It will show up as a new file folder with the photos and Ircat file
From the desktop computer:
1) Connect the external HD
2) Open LR
3) Click on <File>, Import from Another Catalog
4) Find the new folder and open/launch the Ircat file
5) Choose copy files (other options available)
6) Click on <Import>
As mentioned above, during the process it showed that the (HD) Ircat would be copied to the same location as the photos. It did not. The Ircat file (HD) was combined with the main Ircat (desktop computer) file.