Identifying common galaxy spectral lines
You need to compare it with the spectrum of a similar galaxy at a known redshift, that would probably enable you to identify features with known rest wavelengths.

If you can find such a template, then the best way of estimating a redshift for a galaxy spectrum like this, consisting of mostly weak and blended absorption features, is to cross-correlate your template galaxy with this one. The cross-correlation "lag" gives you the difference in redshift.