The windshield washer fluid reservoir on a 2002 Mitsubishi Montero Sport is typically located
under the hood, in the front passenger side corner. It's often a plastic tank, sometimes translucent or slightly see-through, and might have a cap that's easily identifiable with a washer fluid symbol.
However, it's always best to check your owner's manual for the precise location. The manual will have diagrams and clear instructions.