Which of the following job duties would a software developer perform?

A software developer would primarily perform the following job duty:

- **writing the code to make a new application work**

While a software developer may also be involved in aspects of product usability and needs assessment, the specific duty of writing code is most directly aligned with the core responsibilities of a software developer. The other duties listed, such as establishing security procedures and managing data, are typically associated with roles like security engineers, data managers, or system administrators.