AIX now ships with sshd but is not configured to forward X11 by default. In addition it looks like the person who packaged OpenSSH at IBM did not have xauth in the default AIX location.

To enable X11 forwarding on AIX.
#1 Edit /etc/ssh/sshd_config and uncomment:

X11Forwarding yes
X11DisplayOffset 10
X11UseLocalhost yes

Then add an entry pointing to the correct xauth location.

XauthLocation /usr/bin/X11/xauth

#2 Login to your console using your HMC or with telnet - in other words NOT with ssh

#3 Stop and start your sshd. Verify it is down with ps before restarting.

stopsrc -s sshd
ps -ef |grep sshd
startsrc -s sshd

#4 If you are running an X server on your desktop, gui programs on the target AIX server will now send their output to your desktop.