Question

Read the sentence.

Answer 1

in the sentence If you do not want to learn to juggle Matthew will show you where you can wait, the comma should be placed after Mathew due to the fact that another clause will began.

Option A is correct.

Comma may be employed after introductory a) clauses (as in this case), b) phrases, or c) words that come before the main clause.

Common starter words for introductory clauses that should be followed by a comma include after, although, as, because, if, since, when, while.

So, in this case, after the clause started with I. the comma is placed.

Answer 2

If you do not want to learn to juggle, Matthew will show you where you can wait. it would be after juggle because it can be reversed As "Matthew will show you where you can wait, if you do not want to learn to juggle. 
Does it make sense?