There are always a number of places to watch these major sports events online. That is because someone may record the event and this upload to a platform. For instance, there are many games that are uploaded to youtube.
However, you will have to wait a few days after each game is played before they will be made available to the public on youtube. If you want to watch it live or at least sooner, then it will depend on where you live. For example, Afghanistan will be streaming the cricket games for the world cup on hotstar.com. Australia can watch the games on foxsports.com or cricket.com. It seems that the best place to watch the ICC Cricket World Cup 2019 online would be Hotstar.