The bankruptcy trustee does not have the authority to deny or grant your discharge. While any interested party is allowed to challenge your discharge, only the judge can actually deny or grant your discharge.
If someone objects to your discharge, you are entitled to due process. This means you are entitled to proper notice and the opportunity to defend your discharge before the court.
The trustee has a duty under the bankruptcy law to pursue an objection to your discharge if the facts and circumstances indicate to the trustee that you are not entitled to receive it. If this is the case, the trustee will file a lawsuit called an adversary proceeding in your bankruptcy. You will then be served with a summons and complaint by regular mail and be noticed of the time you have to respond.
The case will proceed like any other lawsuit but take place entirely before the bankruptcy court. There may be discovery, such as depositions or document production, and the matter can go before the court for a full trial with evidence and witnesses. The judgment entered by the court will either determine that you are entitled to receive your discharge or that your discharge is denied.