The difference is between whether the modifier is being quoted from Latin (in which case the adjective follows Latin word ordering), or whether the word is being used as Standard English, in which case the adjective follows normal English rules:
He would be known as an emeritus pope.
He would be known as "pope emeritus".
In this case, CNN are using the word "emeritus" as quoted from Latin, rather than as the valid English word, and hence the word "emeritus" goes after the word "pope".
There are some other weird holdovers from Latin that you might come across:
The President elect is due to be inaugurated in January.
Please give a round of applause for our new Professor Emeritus, Professor Stevenson!
As an English learner, generally you should be aware of this rule, but avoid using it yourself except in situations where you have heard it used before. It is rarely used, and you can always substitute normal English word ordering without loss of meaning.