This question doesn’t really have an answer because the Internet, by itself, doesn’t have an amount of data at all. The Internet is a computer network; it transmits data, doesn’t store it. Computers connected to it do.
So you are going to need to define exactly what you mean, such as: all data accessible through the Web? Only data accessible to the public on the Web? Also data accessible through other services than the Web, such as emails on servers with no webmail interface?
Even then one problem with the question is that some data is stored more than once, for example this comment of mine will be federated to several fediverse instances, do you count it once per instance? Once per physical copy made during the operation of that instance (such as backups)? You can see that the question suffers from poor definition.
This question doesn’t really have an answer because the Internet, by itself, doesn’t have an amount of data at all. The Internet is a computer network; it transmits data, doesn’t store it. Computers connected to it do.
So you are going to need to define exactly what you mean, such as: all data accessible through the Web? Only data accessible to the public on the Web? Also data accessible through other services than the Web, such as emails on servers with no webmail interface?
Even then one problem with the question is that some data is stored more than once, for example this comment of mine will be federated to several fediverse instances, do you count it once per instance? Once per physical copy made during the operation of that instance (such as backups)? You can see that the question suffers from poor definition.