A friend of mine will organize an event in London. Because I am living in Paris, I would like to say that
I wish this event was also in Paris.
Do you think that my sentence is correct?
It's fine in spoken English but it's not in written English. It should be:
I wish this event were also in Paris.
If you look into the Collins Dictionary here, you'll find the following explanation:
If you wish something were true, you would like it to be true, even though you know that it is impossible or unlikely.
I wish that I could do that. [VERB that]
I wish it weren't true. [VERB that]