At what energy do extragalactic cosmic rays take over from Galactic ones?
In plain words
Below some energy cosmic rays come from our own galaxy and above it from other galaxies; whether the handover happens near $1e17\,\mathrm{eV}$ or near $5e18\,\mathrm{eV}$ (the ankle, where the spectrum flattens) is unsettled.
Precise statement
Determine the energy at which the extragalactic flux exceeds the Galactic flux, using the iron knee near $8e16\,\mathrm{eV}$, the second knee near $1e17\text{ to }3e17\,\mathrm{eV}$, the ankle near $5e18\,\mathrm{eV}$, the energy dependence of the mean shower depth $X_{\mathrm{max}}$ and its spread (lightest composition near $2e18\,\mathrm{eV}$), and the change of the dipole direction from near the Galactic center below $1e18\,\mathrm{eV}$ to away from it above $8e18\,\mathrm{eV}$. Answer: the transition energy and the Galactic component spectrum, including whether a second Galactic population beyond the knee sources is required.
What would settle it
Mass-resolved spectra and anisotropies from $1e16 \text{ to } 1e19\,\mathrm{eV}$ with overlapping detectors, fit by a two-population model with propagation.