How do I ask for resource donations?

Resources can only be given to you by a trader class member of your alliance. You would need to ask around in your alliance chat if anyone can do this. Alliance members can donate resources in the Shrine building if you have dead troops from the previous week, you need to go to the Shrine and use the 'Request donation' button to enable this.

Alternatively if you mean for alliance donations then you just need to chat or message them to remind them to do this.