Can we file RTI to Trust?
If the said trust receives grants/funds from any government department/ministry, it is a public authority and the RTI Act is applicable to it. Such trusts come under the definition of section 2(h)(i) as they receive funds/grants from the government. You could make a RTI Application to the concerned trust. Various CIC orders have held this position. Under section 2 (f) of the RTI Act, you could obtain certified copies of the relevant documents and records.
Otherwise, you could also make an application to the authorities under which the trust is registered/governed such as the Charities Commissioner amongst others.