Nuclear knockout reactions at relativistic energies provide a sensitive tool to determine the ground state properties of nuclei close to the drip line. Studies with kinematically complete measurements reveal the initial correlations in the reacting systems and yield spectroscopic information on the continuum states populated in the decay channel. The coincident data of charged fragments and neutrons as well allows to unveil the possible influence of the reaction mechanism to the interpretation of the measurements. Two- and three-body correlations can be observed and allow to determine the internal momentum distributions of halo nuclei as well as the assignment of spins and parities to the populated states in the intermediate systems in the breakup process.