Sometimes the action is not listed, sometimes it 's encripted in the rod model, sometimes you can find the action in the manufacturer 's website ( if it has ones ), sometimes the action is labeled on the rod after the rod model.
Example of encription in the rod model:
Fenwick Techna model AV60MM
Decoding.-
Series ( AV )---> AV
Length ( 60 )---> 6 ft
Power ( M )---> Medium
Action ( M )---> Moderate
Shimano Clarus model CSSX66MHA
Decoding
Series ( CS )---> Clarus
Type ( S )---> Spinning
Action ( X )---> Extra Fast
Length ( 66 )---> 6 '6"
Power ( MHA )---> Medium Heavy
Each manufacturer has it 's own way of encrypting, to know what they are talking about you have to know the system the manufacturer uses in order to understand it. Other manufacturers use different types of blank material to manufacture specific types of rods, for example al GLoomis crankbait series rods are moderate action regardless of the power rating, all spinnerbait series rods are extra fast action regardless of the power rating, all dropshot series rods are extra fast action regardless of the power rating and so on, you also have to know that when you purchase a rod from them.
Like Seyone mentioned, you can 't find information about the rod then most probably it will be a fast action.