We are using SVN server 1.4 (I think) with the clients being either the command line client or TortoiseSVN.
                
                A: 
                
                
              
            Check the red book section 'Discovering locks'. I believe it contains the answer.
                  andreas buykx
                   2009-05-12 15:26:18
                
              
                +3 
                A: 
                
                
              
            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").
                  sleske
                   2009-05-12 15:29:37
                
              
                
                A: 
                
                
              
            Using the repo-browser feature of TortoiseSVN there is a lock column that shows the user who locked the file.
Right click on the local working copy -> TortoiseSVN-> repo-browser.
                  Detroitpro
                   2009-05-12 15:30:02
                
              
                +7 
                A: 
                
                
              
            Use svn status --show-updates to discover locks on files. In the following example, Sally discovers there is a lock on raisin.jpg.
$ whoami
sally
$ svn status --show-updates
M              23   bar.c
M    O         32   raisin.jpg
       *       72   foo.h
Status against revision:     105
Once you know the lock, you can use svn -info to discover who set the lock. Notice "Lock Owner" below:
$ svn info http://svn.example.com/repos/project/raisin.jpg
Path: raisin.jpg
Name: raisin.jpg
URL: http://svn.example.com/repos/project/raisin.jpg
Repository UUID: edb2f264-5ef2-0310-a47a-87b0ce17a8ec
Revision: 105
Node Kind: file
Last Changed Author: sally
Last Changed Rev: 32
Last Changed Date: 2005-01-25 12:43:04 -0600 (Tue, 25 Jan 2005)
Lock Token: opaquelocktoken:fc2b4dee-98f9-0310-abf3-653ff3226e6b
Lock Owner: harry
Lock Created: 2005-02-16 13:29:18 -0500 (Wed, 16 Feb 2005)
Lock Comment (1 line):
Need to make a quick tweak to this image.
                  Mike Caron
                   2009-05-12 15:31:41