Moreover, reading code is a skill, and much of being a good developer involves working with other people code, which means being able to efficiently parse other people's code.
Of course we read a lot of people's code, but I'm not so sure it's something that needs to be actively practiced rather than done naturally over a career (which makes recommending people to read code pointless if it happens naturally).
But if all you do at work is line of business apps in VB6 for years on end, then I would recommend reading the source code for some games, database servers, your OS kernel, your favorite text editor, or something unrelated to your job. The point is to expand the scope of the projects that you're capable of undertaking.