The IFMIF-DONES facility, currently under construction in Granada (Spain), is dedicated to testing materials under neutron irradiation, as part of advanced materials research for next-generation fusion reactors. The superconducting linear accelerator of the facility is intended to deliver a continuous-wave deuteron beam with an energy of 40 MeV and an unprecedented current of 125 mA. The production of neutrons is then achieved by driving the 5 MW beam into a liquid lithium target. Beam diagnostics play a critical role in the IFMIF-DONES accelerator due to several unique challenges. These include the extremely high beam power, the harsh environment due to neutron and gamma radiation and the required operational availability of the accelerator. Moreover, the accelerator may operate in pulsed and continuous wave for commissioning and standard operation, respectively. This work presents an overview of the main beam diagnostics techniques and strategies needed to address these challenges, as well as the construction plan and the prototyping works. ACKNOWLEDGEMENT This work has been carried out within the framework of the EUROfusion Consortium.