Assuming you want the holes to be parallel to each other and perpendicular to the flat plate rather than a curved one:
To mark the hole positions on the curved body use the Project tool.
Use the plate as the sketch you will project from and the curved body as the face to project to.
To make the holes through the body, extrude the holes from the flat plate through the body. As simple as that. (When the extrusion reaches the body it should change itself to a subtraction tool and make the holes.)
If you are trying to make a curved plate with parallel holes, copy the plate when it’s flat and offset it away from the main body.
Then curve the closer plate.
Then extrude the holes through it as well as the body.
If you are trying to make the holes converge on the central axis of a cylinder, that will mean using the Subtract tool with the Rotate Around Axis tool.