Its impossible to conceive the objective unless you have the right tools then its easier than the hype makes it out to be. For example take the relationship between color and light. A photon hits your eye, brains interprets that photon as a color (lets use blue as an example). Now lets say due to differences in the brain 3 out of 10 people see red instead of blue. How do we get to an objective truth here? the majority of people see blue but there is minority who sees red instead of blue, whats real and whats not, what is the true nature of the photon. The solution here is to measure the wavelength of the photon, and that is the objective truth in this example, not blue, not red, WAVELENGTH is the objective truth here. We have tools to competently remove subjectivity and get to an approximation of the truth.
Now, i cannot imagine how a post-modernist would solve this, because you would have to take all interpretations into account.