We also have different departments where situations like these sometimes arise, and we always just use our internal company chat for this purpose: the agent with the question sends the ticket link to the colleague who might have the answer, and the colleague replies via chat and maybe adds a note to the ticket. To facilitate this, sales and support agents have access to each others groups in our system.
An IMO nice solution for this would be if Zammad would allow the creation of new tickets via macro, which I’ve already suggested here for a similar purpose. Then you could create a macro “Ask support for help” which would create a new phone ticket in the support department where you put your question in, and the original ticket could be linked to the new ticket.