Question: I found this in an ecological park:

[![enter image description here](https://i.stack.imgur.com/lrDeA.jpg)](https://i.stack.imgur.com/lrDeA.jpg)

*Cola* is actually a Latin word (a scientific one, referring to the plant), albeit its etymology is [African](https://en.wiktionary.org/wiki/cola#Etymology_1).

I am curious about whether it is "probably" the best-known Latin word in the world. If not, which one might it be? 

I think we could agree that *Cola* it is likely to be indeed very well known. We could also agree that it might be impossible to satisfactorily settle the issue of the "best-known" Latin word. Yet, hopefully, by comparing with other well-known words, we could gauge the extent to which that claim is likely to be true or not.

Answer: 
As others already noticed Cola is not originally Latin. It is a loan-word. 

I would presume that Ave (or Amen) would be more appropriate. Every Christian and a lot of other people know those 2 words, which covers probably over a billion people.

And, as far as I know, both are truly original Latin words.
I would figure words like *Rex* (eg: tyrannosaurus Rex, Oedipus Rex) would be better known.