  One-neutron knockout reactions have been widely used to extract information
about the single-particle structure of nuclei from the valley of stability to
the driplines. The interpretation of knockout data relies on reaction models,
where the uncertainties are typically not accounted for. In this work we
quantify uncertainties of optical potentials used in these reaction models and
propagate them, for the first time, to knockout observables using a Bayesian
analysis. We study two reactions in the present paper, the first of which
involves a loosely-bound halo projectile, $^{11}$Be, and the second a
tightly-bound projectile, $^{12}$C. We first quantify the parametric
uncertainties associated with phenomenological optical potentials.
Complementing to this approach, we also quantify the model uncertainties
associated with the chiral forces that can be used to construct microscopic
optical potentials. For the phenomenological study, we investigate the impact
of the imaginary terms of the optical potential on the breakup and stripping
components of the knockout cross sections as well as the impact of the angular
range. For the $^{11}$Be case, the theoretical uncertainty from the
phenomenological method is on the order of the experiment uncertainty on the
knockout observables; however, for the $^{12}$C case, the theoretical
uncertainty is significantly larger. The widths of the confidence intervals for
the knockout observables obtained for the microscopic study and the
phenomenological approach are of similar order of magnitude. Based on this work
we conclude that structure information inferred from the ratio of the knockout
cross sections, will carry a theoretical uncertainty of at least $20\%$ for
halo nuclei and at least $40\%$ for tightly-bound nuclei.
