What type of glue is used to glue the glass top to the iron rod base for this table?  

The glass top
sits on the base and remains in place by the grace of gravity and the care of the resident. Many other glass-top tables rely on this formula; see for instance the well-known Noguchi coffee table . . .
http://www.google.com/search?client=safari&rls=en&q=noguchi+table&ie=UTF...

It can easily slide and fall ...
It can easily slide and fall over if it does not use a certain type of glue

Tables
like this often have a plastic or rubber buffer between the metal/wood and the glass to prevent the glass sliding off.

Perhaps inquire with the manufacturer?
After mulling it over, I suppose I can understand that you might have a legitimate need to secure the top on this table. I spoke too soon and apologies are due.
Unfortunately, whatever you do will result in visual detraction. I'd probably start with RTV silicone, maybe in black.