Can you reapply if denied?

What if someone is denied can you reapply?

No.

Q1: Can I appeal USCIS’s determination?
A1: No. You cannot file a motion to reopen or reconsider, and cannot appeal the decision if USCIS denies your request for consideration of deferred action for childhood arrivals. USCIS will not review its discretionary determinations. You may request a review using the Service Request Management Tool (SRMT) process if you met all of the process guidelines and you believe that your request was denied due to one of the following errors:

USCIS denied the request for consideration of deferred action for childhood arrivals based on abandonment and you claim that you did respond to a Request for Evidence within the prescribed time; or
USCIS mailed the Request for Evidence to the wrong address, even though you had submitted a Form AR-11, Change of Address, or changed your address online at www.uscis.gov before the issuance of the Request for Evidence.

Source

Question really is what if you are approved 1-821D (Deffered Action for Childhood arrivals) but denied i-765, can you then reapply for work authorization?

If it works like TPS you might be able to appeal the decision.

If you are denied for DACA. You cannot appeal, you can re-apply but you will be denied again.

There's no mention about work permit denials, once you get deferred action, work permits become a whole different issue.

Tricky situation. It does not explicitly state you cannot start a new case. A Lawyer can't help, we need more clarification from USCIS in this one.

Pretty much, I've been looking everywhere and I can't find anything on the issue. Step 5 in the TPS filing process is the closest thing there is.

^might be one of the reason why in your Biometrics appointment the receipt number matches your i-765 application, and since Biometrics are for DACA, I can only determine once your DACA is approve so is your i-765, then again i can be wrong... we need more clarification from USCIS.

That's because form i-765 requires a background check. The receipt number is just your case number, you could get RFEs, denials, interview appointments, etc with that same number--it really doesn't mean anything.