How do I add a link to a menu from a module in Drupal 6?
You are using a wildcard in the path node/%node/jobs. If you want Drupal to show a menu link, you have to tell it how to figure out the %node argument. You can do it with a function named node_to_arg. 

The function name, actually, is [wildcard]_to_arg. I suggest you change the wildcard to something different, since there are several menu paths with %node in it. If you relied on node_load to return you a node object, you can just call it from [wildcard]_load.

There is documentation on [wildcard]_to_arg and you can see how user_uid_optional_to_arg implements it for the user/%user_uid_optional path.