Is the following sentence missing semicolons or commas? If so, where?: Tim went to the candy store quite often the clerk even knew his name.
after quite often.
"After quite often", you should use a semicolon as it is a new clause and it can be an independent clause too.
Like--"Tim went to the candy store quite often; the clerk even knew his name."
You can also use A COMMA , but you should use a connecting word like AND, before it, COMMA is --this is a rule if two clauses are strong, we use a connecting word having a COMMA. These are architecture of a sentence making.
"Tim went to the candy store quite often, AND the clerk even knew his name."
More, if the two clauses are short, a writer may not use any comma before connecting word.
Like, life is short but art is immortal.
Another possibility is, you can use "that" clause which means your the second clause is a non restrictive clause ( not essential if you don't mention it)
So, the sentence is like it---"Tim went to the candy store quite often that the clerk even knew his name."
What should you do?
Practice and practice following good writers or authenticated sources of grammar day by day. Don't think Rome was built in a day!
CAUTION: Punctuation rules are important to know the sentence structure, just keep in mind.
You have to be careful about AP style or Oxford as they both follow a bit of different rules too.
Again question of practicing, do it.