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The command line client shows the lock owner with the command "svn info".
In TortoiseSVN, you can see the lock owner in the "properties" context menu (tab "subversion").
Steps to check:
Right click on the file/folder on which you want to determine the lock
Go to TortoiseSVN Options >> Repo-browser
A new window will open and you will get a table view
Lock column in the table will show who has the lock