What computer application or implementation requires the most lines of code?

The number of lines of code isn’t really a direct cause of accomplishment. The more code, frequently the more complex and harder it is to achieve a complex solution. And how one measures lines of code is also not really a simple thing. But it is true that complex and large projects may end up with lots of code.

I don’t think there’s an answer to the type of question as you’re putting it, since it’s not really true that task X necessarily requires N lines of code. At most, some example of a project that does X may at some point involve N lines of code.

Database size isn’t particularly a problem of storage space, but what does become a problem is having so much data that even complex software can’t find or correlate the interesting parts of it. Government and corporate data from spying on citizens tends to fall in that category. They record as much data as they can about our communications, movements, health, transactions, biometrics, voices and faces and so on, but it’s so much data that the task of finding interesting useful bits becomes the challenge.

The “matter transporter” would mainly be a matter of technology, not so much of computation.

It also depends on the language used. For example a high level language like basic or C takes only 1 line of code to print hello world on the screen where as a low level language designed for a specific processor like assembly will take 7 or more lines to achieve the same thing. However a program in assembly will tend to execute much more quickly.

As I understand it, weather forecasting code is incredibly complicated because of all the variables it has to deal with. That would be a prime example.