Are two prepositions allowed along with one another in the English language?
For example:
An opportunity will happen on through any doors
Are two prepositions allowed along with one another in the English language?
For example:
An opportunity will happen on through any doors
There are some cases, but they are mostly idioms or set phrases.
The most obvious I can think of is "over in" (which really means "over there in")
There are five cars over in the garage.
But your example doesn't make any sense - especially since 'on' is a preposition indicating location, while 'through' indicates direction.
Since a preposition normally governs a NP (noun phrase) the general answer is No.
There are many examples of sentences containing sequences of words that could all be prepositions (for example, anything containing the phrase "put up with"). But on inspection, only one of the words ('with', in that case) is being used as a preposition.
So your example is not grammatical. In fact, when I read it, I try to make the "on" something other than a preposition, and wonder if there is a phrasal verb "happen on". (There is one, a transitive phrase meaning "find by chance", but it doesn't make sense here).
As @ColinFine answered, the general answer is no. However, there are some idiomatic usages with two prepositions such as
He stole it from under my nose.
The cat came from under the desk.
Some more examples: from behind, from beneath, etc.
There are other examples such as out of and off of as in "Get out of here." and "Get off of my back." but some people say that out and off are not prepositions.