Is it safe to click on the link? Under what conditions will the script be triggered?
It should be safe to click (although I still wouldn't).
It looks like the attacker tried to exploit the shellshock vulnerability. If your server is vulnerable, the script will already be executed, you calling it again doesn't add that much harm (in this case, you don't have any more rights than the attacker has, assuming you are not viewing the log from the server).
Of course, clicking the link doesn't gain you any knowledge either, and generally, it's a bad idea to click on links in your log (because of XSS), so don't click on it, and check if you are vulnerable to shellshock.