Yes, the James Webb Space Telescope (JWST) should be able to tell the difference between an exoEarth and an exoVenus. One key difference between these two types of planets is their atmospheric composition. ExoEarths are expected to have atmospheres that are primarily composed of nitrogen and oxygen, while exoVenuses are expected to have atmospheres that are primarily composed of carbon dioxide.

JWST is equipped with spectrometers that can detect the presence of different molecules in an atmosphere, so it should be able to distinguish between an exoEarth and exoVenus based on their atmospheric composition.

Other differences that could help distinguish between an exoEarth and exoVenus include their surface temperature, size, and density. ExoEarths are expected to have surface temperatures that are similar to Earth's, while exoVenuses are expected to have much higher surface temperatures. ExoEarths are also expected to be smaller and less dense than exoVenuses.

JWST can measure the brightness and color of an object, which can be used to estimate its temperature and size. JWST can also measure the transit time of an exoplanet, which can be used to estimate its density.

It is important to note, however, that distinguishing between an exoEarth and exoVenus can be difficult, and JWST may not always be able to make a definitive determination. Further observations with other telescopes may be necessary to confirm the nature of an exoplanet.