No question in English grammar is ever trivial to someone who really wants to master it. Now, regarding your two questions:
1. There are three possible ways of punctuating the adverbial modifier “if any” depending on its position in the sentence:
(a) Frontline position – “If any” followed by a comma. Example: “Some friends of mine may come tonight.
If any, tell them I’ve gone ahead to our meeting place.”
(b) Inserted position – “if any” set off by a pair of commas. Example: “How many pairs
, if any, do you want of these special running shoes?”
(c) Tail-end position – “if any” preceded by a comma. As in your example: “How much do you send to your family in the Philippines
, if any?”
If you think the matter at hand is not particularly important or is only a trivial or remote possibility, you can enclose “if any” in parenthesis. Example: “Please indicate number of pets
(if any).”
2. Words set off by double dashes are known in English grammar as
parentheticals. Depending on the grammatical form of the parenthetical, it can behave as a modifier or qualifier, as an intensifier, as an interrupter, or as an interjection. Parentheticals actually take many forms and many roles in a sentence and may even need different forms of punctuation, so I can’t give a simple answer to your question about their behavior. Instead, I suggest you check out and study the following discussions about punctuation in general that I had previously posted in the Forum:
Part I – “A unified approach to the proper use of punctuation in English”Part II – “A unified approach to the proper use of punctuation in English”Part III – “A unified approach to the proper use of punctuation in English”For good measure, I suggest you also read the following essay that’s also posted in the Forum:
“A grammar conversation on parenthetical usage”I’m sure that when you’re done, you’ll have mastered not only the usage of double dashes but the usage of punctuation in English as a whole.
