The Honolulu Department of Planning and Permitting (DPP) oversees permitting and enforces the rules on ADUs.
They put together some ADU instructions, which describes the basic requirements and permitting process. Also included in these instructions are answers to frequently asked questions and the ADU pre-check form.
The DPP circulates your pre-check form through the relevant agencies.
For contact information for the different divisions within the DPP, visit the their contact page.