Yes. A Dojo must always be free for attendees. However if a Dojo requires sponsorship for a specific purpose they can ask parents for an optional donation. This should not be done in a manner where parents of attendees who are unable to donate feel excluded. An example is to make the announcement to parents informing them of what the donation is needed for. Then leaving a donation box at the side of the Dojo for a session or two.
Suggested donations are not permitted as a method of fundraising. If a donation is suggested (e.g. $2 per session) this puts more pressure onto parents and young people who cannot afford to attend. Suggested donations are construed as an applied 'fee' and are considered a breach of the CoderDojo Charter.