  We find soft X-ray emission lines from the X-ray binary Swift J1858.6-0814 in
data from XMM-Newton-RGS: N VII, O VII and O VIII, as well as notable residuals
short of a detection at Ne IX and other higher ionisation transitions. These
could be associated with the disc atmosphere, as in accretion disc corona
sources, or with a wind, as has been detected in Swift J1858.6-0814 in emission
lines at optical wavelengths. Indeed, the N VII line is redshifted, consistent
with being the emitting component of a P-Cygni profile. We find that the
emitting plasma has an ionisation parameter $\log(\xi)=1.35\pm0.2$ and a
density $n>1.5\times10^{11}$ cm$^{-3}$. From this, we infer that the emitting
plasma must be within $10^{13}$ cm of the ionising source,
$\sim5\times10^{7}r_{\rm g}$ for a $1.4M_{\odot}$ neutron star, and from the
line width that it is at least $10^4r_{\rm g}$ away
($2\times10^{9}(M/1.4M_{\odot})$ cm). We compare this with known classes of
emission line regions in other X-ray binaries and active galactic nuclei.
