Strange requests to web server

It appears that your server is the target of an automated attack involving the ZmEu scanner.

That first request appears to be from another automated attack involving the Morfeus Scanner.

That last request appears to be an attempt to exploit vulnerabilities in the Home Network Administration Protocol (HNAP) implementations of D-Link routers. More information about the attack can be found here.

From a cusory glance at the request it's making, I'd say you have nothing to worry about if you aren't running phpmyadmin on your systems. Such attacks are commonplace for servers connected to the internet and the scans are getting 404's indicating that your server does not have what they are looking for.

Every server that is connected to the Internet will receive hundreds of "weird requests". Most of them are from automatic botnets which try to replicate, by finding machines which feature a specific vulnerability. They try random IP addresses (there are only four billions of possible IP addresses, after all). So yes, someone is trying to enter into your server, but that "someone" is a mindless automaton who has nothing against you, specifically.

I would say that if you find the log entries, then the attack did not work so you don't have to worry about them. When the attack is successful, the first thing the attacker does is to remove its traces from log files.

This does highlight the utmost necessity of installing security fixes, because every online server is, by construction, exposed and will be targeted by such random attacks at some point.

if you want to block known scanners you might want to use nginx-based WAF naxsi + doxi-rules; these scanners are widely known