Is there a way to export detailed data about atom connectivity, dihedral angle, etc from GaussView?
To my knowledge, neither .xyz nor .com format preserve connectivity information by default. Gaussview (and many other programs) makes an educated guess based on atomic covalent radii and positions of atoms. Gauss .com may also store a set of internal coordinates used for optimization that gaussview derive from connectivity information. Gaussian .com may contain connectivity information if geom=connectivity option was used, but you cannot expect it. The format of connectivity section is documented in geom=connectivity suboption part of Gaussian input docs.

That said, some other formats like .pdb allow to store that data explicitly and are well documented. Also, Gaussian can be used to perform various forms of population analysis printing a lot of nice tables, some of them might be interpreted as connectivity information (then again, some cannot).