it can be done in these tables: ow_newsfeed_activity ow_newsfeed_like in your database

How ? By deleting the tables ?

not tables, certain rows, which corresponds to a certain likes and comments

If I delete them maybe I get errors

Don't worry, there won't be any errors as it is just a user data in the newsfeed

Hi, Ive been wondering about this too. Id like to make sure that likes notifications never go on the newsfeed. I think the advice you gave means I can delete specific notifications, but not all automatically.

Any idea how I can make sure no notifications never go on the newsfeed?
Thanks

This is considered as a custom code modification. 

Ok thanks, how much do you think it might cost?

Unfortunately, I can't tell you even a ballpark figure.