Job title is not quite correct. Your "job title" is what your employer chose to put on your contract, and is on your business card and email signature. "Job titles" are therefore industry (and even company) specific.
The subscribers to your magazine may or may not all be from the same industry, but there's still no guarantee of consistency of job title. What one company calls a "Marketing Director" another company might call a "Vice President - Marketing" and still another might simply call him a "Partner" (and it just so happens that his particular role is marketing).
So, I would suggest either Job function or Job role.
Job function is the routine set of tasks or activities undertaken by a person in that position. An employee's title and function are often closely related, though not all job functions are clear based on title alone.
A "job role" is a description of what a person does. A "job title" is a convenient name for a role.