For the Coach Training, depends if you want it in french. If so, I am the one organizing it and I will definitely schedule it soon. The pre requisite is to attend a Practitioner Training though... We cover a lot of the basics during that training as your colleague may have told you.
Re your question, I will give you the wording in french since it seems like your native language: https://igipartners.com/constitution-holacracy#art323 (for english speakers: https://www.holacracy.org/constitution#art323)
“3.2.3 Tester les Propositions
Le Facilitateur peut tester la validité d’une Proposition en posant des questions au Proposeur. Pour que la Proposition passe le test, le Proposeur doit être en mesure de décrire la Tension et de donner un exemple de situation réelle, actuelle ou passée, dans laquelle la Proposition aurait déjà permis de réduire cette Tension et d’aider le Cercle de l’une des manières autorisées par la section précédente. Le Facilitateur doit abandonner la Proposition s’il estime que le Proposeur n’a pas rempli ces conditions.
Toutefois, pour évaluer la validité d’une Proposition, le Facilitateur peut seulement juger si le Proposeur a présenté l’exemple et les explications qui sont requis, et si ceux-ci ont été présentés selon un raisonnement logique et sont donc raisonnables. Le Facilitateur ne peut pas porter de jugement quant à leur exactitude, ni juger si la Proposition est susceptible de traiter la Tension.”
It is not written when the Facilitator can do that but since he cannot infringe the process, just like anyone, the obvious step to do it is during Clarifying Questions. During that step, I may, as a Facilitator, ask questions (like anyone) like: “could you remind us your tension underline this proposal?”, or “which role is limited by the tension you are feeling?”. If, given the answers, it is clear that the tension doesn't limit one of the person's role, I would ask: “did you get permission from the role who is limited by this tension to process it?” (here we are not talking about the role stated in the proposal but the role who should feel the tension because if you are allowed to process a tension for the sake of another role because he gave you the permission to, it is ok). If, that person is not authorized or doesn't have a concrete situation, it is a “mental” tension, based on speculation or nothing, just a good idea, than I have the clue that it doesn't respect the constitution's criteria of a valid tension to be processed in a governance meeting and I can drop the item directly. As a Coach, I will also give a bit of explanations here, this is why it is crucial to get support from a Coach, otherwise people will feel like the Facilitator can drop any proposal when he wishes to.
Again, as a Facilitator, you have to be neutral and seek for an argument without judging it. If the person says: “yes it does limit my role X”, you can't judge whether it is true or not, all you can ask is: “ok, what specifically? the purpose? which accountability?”. You are a curious scientist trying to help the person figure out whether it is a valid tension to be processed or not.