spectra - Reference for broader spectral lines?

Both potassium (766.5+769.9 nm) and sodium (818.3+819.4 nm) have strong resonance lines (doublets) in this part of the spectrum. There are also the calcium triplet lines at 849.8+854.2+866.2 nm.

These are the strongest atomic absorption lines seen in the spectra of solar-type stars or cooler at 700-900 nm.

A more specific answer would require the spectral type of the star.

To do something more general and/or extensive you would need to get hold of a good line list (a line list alone cannot easily tell you which lines will appear strongest in a stellar spectrum) and a spectral synthesis programme like SME or MOOG.