Always use the plural "are" with a plural subject (e.g. "question"), and the singular "is" with a singular subject (e.g. "article"), or with an uncountable subject (e.g. "water"). Hence:
Is there any question I should be asking?
Are there any articles available on the subject?
Is there any water left in the pond?
The following are never correct:
Is there any questions I should be asking?
Are there any article available on the subject?
Are there any water left in the pond?
You might be interested in the related topic of the presentational construction.
In form, the presentational construction uses the dummy pronoun "there" as subject but some other verb than BE as the main verb. E.g. "There remain only two further issues to discuss"; "There seems little doubt that the fire was started deliberately."
Some verbs (and verbal idioms) in this construction are: appear, arise, arrive, develop, emerge, enter, escape, follow, grow, lie, live, loom, occur, persist, sit, spring up, sprout, stand. Many of these verbs have to do with being in a position or coming into view.
Most presentational clauses are of the bare type or have a locative extension. (But there are exceptions, e.g. "There remain only two further issues to discuss."; "There remained only two officers alive.)
There are some differences in pragmatic constraints between presentationals and existentials. One difference is that definite noun phrases occur more readily as the "displaced subject" in presentationals than in existentials.
Note: The info and examples in my post are borrowed from the 2002 reference grammar by Huddleston and Pullum et al., The Cambridge Grammar of the English Language, pages 1402-3.
Best Answer
The subject is clearly what.
Fairly recently, some linguists have chosen to call there the subject in simple existential sentences, like this:
But this causes problems, as in your example. The main reasons why they seem to want to label there the subject are that it is the first word in a simple existential sentence, and that, colloquially, singular is can be used even when there are several things in the room:
Another problem is that it results in a completely different analysis of two extremely similar sentences, both in construction and in meaning:
Here everyone agrees that one person is the subject.
This is exactly the same sentence, both in meaning and in syntax, except that the adverb there was added, which comes in the first position and causes subject-verb inversion, just as in (some) other Germanic languages.
(In English, this only happens with some words, like there, but in German and Dutch it happens with any non-subject in first position: Ich bin heute in Berlin (normal order) → Heute bin ich in Berlin. (inverted because heute is in first position).)
Why should one person suddenly no longer be the subject? Why should the verb be keep its exact same meaning but suddenly acquire completely different arguments? Occams Razor says no.
By the same logic of those linguists, the first constituent in this sentence should be the subject, just like there above; after all, it comes first, before the verb. It would be confusing to analyse this sentence differently from there is one person today, since they clearly have the same structure. But noöne would suggest this: everyone agrees that in this room is adverbial here and one person the subject.
Further, it seems strange to call a non-noun like there a subject.
Lastly, in languages where adverbs and subjects are more clearly marked as such, by affixes and endings, there is never considered the subject in similar sentences. Doing so in English would cause a rift between the analyses of the same construction in different languages. Both Occam's Razor and those who are learning linguistics would be displeased at such inefficiency. The same applies to comparing the use of the same construction in older English and modern English.
The simplest analysis is to say that there is always an adverb in existential sentences, but that in some such sentences the verb can become singular colloquially. There are many other exceptions where verbs seem to have a different number from their subjects, so this shouldn't be too shocking.
Who is clearly the subject here. Replace it with a personal pronoun and it is plain to see:
He can only be subject (complement).