Learn English – Formal way to say “pay off”

How about simply translating née into English, giving born?

"Jane Smith (born Doe)"

For an example of usage, see this web page

Additionally, see this definition (1b): used for saying that someone had a particular condition, personal quality, name, or social status at the time when they were born [...] e.g. Elton John, born Reginald Dwight.

You may be able to reuse some terminology from software world here.

There is a standard software design pattern called Observer and its terminology may help. Quoting wikipedia:

The observer pattern is a software design pattern in which an object, called the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods.

Also there is a Observable interface which may be implemented by observable objects. Quoting its description:

An observable object can have one or more observers.

[I know subject was a previous answer but I think this was too long as a comment.]