There are several online sources of spectra (eg SDSS), but they usually just provide a FITS file with data, or a plot vs wavelength without any annotation. Of course, you could use the NIST atomic spectra database to identify lines, but that quickly becomes tedious. There are many figures containing spectra for various classes of stars in the book by Gray and Corbally, Stellar Spectral Classification. Many of these figures were previously available on Gray's web site, but the links no longer work. I scanned one that may be of use, Figure 7.1 containing spectra of G through K stars. In particular, one of these spectra is for a reference standard G0V star, $\beta$ CVn, with the stronger Ca, Fe and H-Balmer lines identified. Another good resource for annotated spectra of many star classes is Richard Walker's, Spectroscopic Atlas for Amateur Astronomers. I have the printed version, but pdf files of older versions are available online. This atlas contains spectra of a G0IV star, and the Sun, G2V, that have similar absorption lines. There are also collections of standard spectra, such as the Miles library. These are often included in software used for processing spectra, along with tables of common lines for various elements that can be shown on the plot. Programs I have used for amateur spectroscopy that display these include Rspec (commercial), Vspec and ISIS (Christian Buil).