$ ls -l ~/.local/share/applications/zotero.desktop
lrwxrwxrwx 1 terdon terdon 14 May 29 11:33 /home/terdon/.local/share/applications/zotero.desktop -> zotero.desktop

ln source target

rm ~/.local/share/applications/zotero.desktop
ln -s "$PWD/zotero.desktop" ~/.local/share/applications/

$ tree
.
├── file
└── foo

1 directory, 1 file
$ ln -s ../file foo/
terdon@tpad foo $ tree
.
├── file
└── foo
    └── file -> ../file