Where can I find information about the mission and day-to-day tasks for UIC W3YTAA, Senior Leaders FRG, at Fort Eustis?

That because when you're placed on assignment the UIC is a replacement UIC for incoming personnel, not an actual unit. Whatever the word portion of your projected unit says is where you're going

By the MTOE for TRADOC HQ, there are three 88M positions in TRADOC HQ. Two -20 level(SGT) and one -40 level (SFC). One of the SGT positions is with the DCG/COS, and the other is the Exec. office. Your best bet is to get with your sponsor. Their info should be available through the sponsorship dashboard on ACT, if they haven’t contacted you already.

Log on to ACT and see if you have a sponsor. If you do, your sponsor will be from the unit you are actually going to. It will also have POC's that you may get in contact with.