Put the following in your .vimrc
" WSL yank support
let s:clip = '/mnt/c/Windows/System32/clip.exe' " change this path according to your mount point
if executable(s:clip)
augroup WSLYank
autocmd!
autocmd TextYankPost * if v:event.operator ==# 'y' | call system(s:clip, @0) | endif
augroup END
endif