Wikipedia:User contributions

• if it is a user with a user page: bring up the user page, click "User contributions" in the sidebar or bottom bar.
• if it is a user with a login name but without a user page: clicking on the name in Recent Changes or Page History brings up an edit box for a user page; press Cancel and click "User contributions" in the sidebar or bottom bar.
• if it is a user without a login name and without a user page: click on the IP address in Recent Changes or Page History, it gives the User contributions directly.

Also, you can copy the URL:

/w/wiki.phtml?title=Special:Contributions&target=XX , where XX is the user name or IP address.