When I run the svn command line from the Jenkins shell I get this error:
D:\\Jenkins\\jobs\\Merge Trunk to Stable\\workspace\\stable>svn up --trust-server-ce
Pretty old question, but still quite alive.
As you know, the problem is that the accepted certificate cache (as well as the username/password cache) is per-user, and since Jenkins is running as a different user (most likely SYSTEM), it has no idea of your regular user cache.
Not all SVN clients let you do the "echo p" thing there (it didn't work for me), and the --trust-server-cert apparently doesn't work in this case either.
What worked for me was to open a console window as SYSTEM, and do the interactive acceptcertificate-login-password dance in there.
Since all of this is cached, you only need to do this once, and from then on, all svn up and similar requests will work.