Context. The properties of NGC 7009 knots are investigated by employing UV-to-near-infrared data from the X-shooter spectrograph. NGC 7009 is a widely studied elliptical planetary nebula (PN) that exhibits a pair of knots. These structures belong to the category of low-ionization structures (LISs), which are characterized by enhanced emission from low-ionization species and whose origin remains enigmatic. Aims. Our main goal is to conduct the first dedicated spectroscopic study of LISs in planetary nebulae that covers a wide spectral range from the UV to the near-IR, simultaneously. As a pilot study, we focus on NGC 7009 to investigate its ionized, atomic, and molecular gas, aiming to better characterize the physical properties of its LISs and explore their largely unexplored molecular content. Methods. We obtained spectroscopic data with the X-shooter spectrograph, covering simultaneously and under the same conditions a spectral range from 300 nm to 2.5 μm. The spectrum was processed through the ESO Reflex pipeline, and the physical properties of LISs were derived with the latest version of PYNEB. Results. More than 250 emission lines were detected in the spectra of NGC 7009 LISs, including rare, forbidden transitions from low-ionization species such as Fe+ and Ni+, which have only very recently been identified in the spectra of LISs, as well as two transitions from P+, identified here for the first time in LISs. The detection of multiple shock tracers, together with the shock excitation of [Fe II] and [O I], as revealed by emission-line diagnostics, supports the presence of shocks at LISs. The richness of the spectrum allowed us to derive electron temperatures and densities at the LISs using both collisionally excited and optical recombination lines. In the near-IR spectrum of the LISs, nine ro-vibrational H2 emission lines were detected, seven of which were reported here for the first time in NGC 7009. These lines were used to construct the H2 excitation diagram, providing new insights into the physical conditions of the nebular gas. The excitation of molecular hydrogen is most likely dominated by collisional processes through shocks. Finally, the estimated lifetime of H2 at LISs is approximately 5.0 × 104 years for K1a (East LIS) and 6.6 × 104 years for K4 (West LIS).