conocer- use of subjunctive v indicative
I'm continuing along preparing for DELE exams and I need to clear up some doubt as to the use of the indicative/subjunctive mood for the verb conocer. I understand in the affirmative, the indicative will always be used- eg Conozco a un buen restaurante indio que sirve Pollo al Tandoori.
However, in the negative form this can be a little confusing.
Doing previous exams at home, I came across these two sentences.
No conocía a ninguno de los que estaban en la fiesta, no debían de ser de aquí.
I answered (incorrectly) this question, changing estaban for estuvieran. Similarly, another question appeared in this form-
No conozco a ninguno de los que me has nombrado. Pregúntale a otro.
I answered ninguno (this is where the blank was) correctly, but immediately noticed the form of the verb haber in indicative (has).
What I'd like to know is there are certain forms referring to doubt, eg
Busco una secretaria que hable inglés.
I know the subjunctive is appropriate here because it's not certain that such a secretary exists. However, wouldn't that rule extend to a sentance like this for the verb conocer
No conozco a nadie que pueda arreglar el asunto.
I trust in this last example I used conocer correctly in the negative as an extension of the previous rule (que hable inglés). Could somebody confirm that the two examples for the DELE exam further above use indicative because they are events that indeed occurred and my confusion about use is only due to the mood of doubt when something/someone may or may not exist.
Any help greatly appreciated. My grammar books don't shed any light on this.
2 Answers
There at a couple of issues at play here: First, forget about doubt in relative clauses, the main concept is whether or not the antecedent is specific. Second, conocer is used with two different meanings here: To know the identity of someone, i.e. to be specific about their identity, and to be familiar with someone, as in having them as a friend.
Let's go through the examples:
No conocía a ninguno de los que estaban en la fiesta, no debían de ser de aquí.
The identity of the ones who were at the party are known and specific. Indicative, then. None of them were your aquaintances, but that's not relevant.
No conozco a ninguno de los que me has nombrado.
Same. He named a few specific people, like Tom, Dick and Harry.
Busco una secretaria que hable inglés.
Here the secretary is unspecific. Any secretary will do, as long as he or she speaks English. If you had a specific secretary in mind, like Betty, you could say "Busco a una secretaria que habla inglés". Here you would use her English speaking ability as a tool to help your listeners know who she is.
No conozco a nadie que pueda arreglar el asunto.
Unspecific again. You don't have anyone specific in mind, by definition. The negative antecedent, as in this case, will be followed by the subjunctive as an extension of the concept of being unspecific.
Hope this helps! 
I think the difference between:
No conozco a ninguno de los que me has nombrado.
and
No conozco a nadie que pueda arreglar el asunto
is the relative pronoun que, which with No conozco seems to trigger the subjunctive. If your first sentence had been:
No conozco a ninguno que pueda nombrármelos. Then that would justify the subjunctive.
