What constellation would the Sun be in from an exoplanet? Where would it be in the sky from Proxima B (planet near Proxima Centauri) for example?
The sun would appear roughly half-way between Capella and the W of Cassiopeia. The constellations are a human invention, and don't correspond to actual groups of stars. Since all the nearby stars would be in somewhat different positions the constellations would be mixed up, for example, Sirius would be close to Betelgeuse. You can't really talk about constellations except from the perspective of Earth, but you could say that the sun would be near some of the stars that form Perseus and Camelopardalis.

From more distant exoplanets the constellations would be completely mixed up, so there would be no sense in describing the sun's location in terms of a constellation. The sun would also be too dim to be seen with the naked eye from many exoplanets.