If you do not have proof now, you can submit proof later after your trademark is submitted to the Trademark office. If you do it later, you will need to pay a $100 government fee (for US trademarks).
Will the trademark be owned by an individual or an entity such as a corporation or LLC?
Identify the owner of the trademark. This is the person or organization who will be the owner of record. If you choose individuals, you can enter as many names as you want who own the mark. With an organization, you will have to identify someone to be the person of contact for the organization.
Primary Class 1 - $350