Which table contains this information?
It is the routes table of the NavData.db3 database
Is it possible to sort the table?
Yes, just click on the column title bar in the Database Explorer - the actual sort can take some time due to the number of records. It will look like it has frozen, but just give it time.
If I update the data for EGNT flights how can I propagate this to other users?
Just give them a list of the routes as a txt file
How can I copy data from the database tables to the Windows scratch pad for onward copy to other files, programs or messages?
You can't do this with the Database Explorer. You will have to use an external SQL program and produce an SQL query then export the results. There is no easy way to get these records back into another version of NavData.db3 without using such a program to import the records.
You could send the other users your whole NavData.db3 file, but then they would loose whatever aircraft details they had autopopulated.
If you do decide to play around with your database files, do make a backup first as it is very easy to corrupt SQL files.