So first of all "King and our teacher" is not a subject at all, it is the object of the preposition "of", as written above. Of course it also isn't a complete sentence. But I think what you are probably thinking of is that the "king and teacher" is a parenthetical, set off by two commas. Let me use a simpler sentence:
Looking forward to the appearance of, the king and teacher, Mr Jones.
Here "the king and teacher is parenthetical, and is used to describe Mr Jones. Both commas are required. In that case it is plainly singular. However, the sentence is kind of ugly; it would be better to put the parenthetical at the end "... of Mr Jones, the king and teacher."
However without a comma after "of" Mr. Jones is just stuck on the end, and it doesn't make much sense except if, as a commentator suggested, it is the the name of the interlocutor. (Though that is hard to tell because this isn't actually a sentence at all, having only gerunds and no verb.)
Another option might be that the comma is an indicator of apposition, in which case the of object of "of" would potentially be plural. In this case "our teacher, Mr. Jones" has the two nouns in apposition, meaning the refer to the same thing. So here the preposition might refer to the king, and also a separate person "the teacher" whose name happens to be Mr. Jones.
However even in this case it is perfectly possible that King and teacher refer to the same person, called Mr. Jones. So, if this is the case, it is still ambiguous.
In the case where you insert it parenthetically the ambiguity is resolved by the fact that it is one person, so King and teacher both refer to the same person, Mr. Jones. If it is addressed to the interlocutor (with no comma after of) then it is ambiguous as to whether the object of the preposition is singular or plural.
Context would be required to resolve the ambiguity.