I have the same configuration, on a WAGO CC100 with firmware version 21 it works, on a WAGO CC100 with firmware version 23, all DNS request made from inside the container timeout. Even when deactivating the firewall completely, it does not work.

To reproduce, install docker on WAGO CC100 with firmware revision 23 and do the following commands in a SSH connection:

root@CC100-XXXXXX:~ docker run -it --rm alpine
/ # nslookup www.wago.com
;; connection timed out; no servers could be reached
/ # exit
root@CC100-XXXXXX:~ nslookup www.wago.com
Server:		213.221.143.240
Address:	213.221.143.240:53

Non-authoritative answer:
Name:	www.wago.com
Address: 104.18.154.41
Name:	www.wago.com
Address: 104.18.155.41

So DNS works natively, but not inside Docker containers.