You can estimate both by comparison testing.

For aperture, photograph a uniform target such as a gray card in steady light. Take reference shots with a camera you trust, using known apertures, then make Holga exposures under the same lighting. Compare brightness and find which reference exposure matches most closely. One community answer also notes that some Holgas effectively behave closer to about f/13 because another smaller opening in the light path can limit the lens, making the aperture switch less meaningful.

For shutter speed, compare motion blur. Photograph something moving at a known or steady rate, such as a spinning wheel, and compare the Holga image to reference images made with a known camera at different shutter speeds. The blur length that matches best gives you a good estimate of the Holga’s shutter speed.

If you want a direct measurement, a light sensor can also be used to time how long light passes through the shutter, but for a Holga, practical comparison tests are usually accurate enough.