The construction 'to get + object + past participle' has two uses: 1. The construction which is taught in all the grammar books is the one you refer to as a passive. In fact, this is a causative rather than a passive construction. We use it when you arrange for another person or organisation to do something for you. It's commonly used with reference to professional services, for example 'It was too much work to do on my own, so I got the job done by a local building company.' 2. There is also another more idiomatic use which is rarely taught, but is probably just as common among native speakers in informal situations. We use it to refer to the successful completion of a task which might be lengthy or difficult, or perhaps just dull and unappealing. The implication is that this task presents some kind of challenge. Here are some examples: I'll phone you as soon as I've got my essay finished. I like to get all the housework done before I go to out in the evening. In both of those cases, it is the speakers themselves who do these jobs. As you can see, this use is completely unconnected to the causative use above.

Although "nobody questions my ability to get the job done" is in a form that makes it sound like the passive voice, there is nothing passive about it. "Get the job done" does mean literally what it seems to mean, i.e. to finish or to complete a task, but it is in fact an idiom. It means not only that I have the skills/ability to do the job, but that that I have the will to see it to completion.

This is complicated to explain. To get something done is a description of what the passive voice is used for i.e. to show that you got something done by someone else rather than a description of the form it takes which is generally - I had my hair cut etc. It can be used for the passive itself using by e.g. I got the job done by the company down the road. In the sentence you mentioned, it essentially means my ability got the job done but we don't put it that way.

briefly he wants to say to make the job be done