Using Activity Monitor and viewing Disk Activity, I’m having continuous and what may be excessive Data Reads on an external HD.

In the columns, what column should I be concerned about to find out what Process Name may be the culprit?

Might just be spotlight indexing things. If so I think that process is called mds.

If it does indeed prove to be Spotlight, that continual activity would indicate a corrupt Meta Data Spotlight file (hence MDS). Far more likely to happen if you keep one or more external drives connected.

You can use Onyx to delete the Spotlight file on the external, forcing Spotlight to rebuild it. This can take a fair bit of time so walk away while that is going on.