What is a Multi-Domain Task Force?

Simply put, the A2/AD that MSG (Join to see) referenced is an opponents attempts to keep us, or limit us, from conducting operations in an area. The opponent will used integrated operations in all domains (air, land, maritime, space, and cyberspace) to deny, or restrict, our ability to operate before, leading up to, and during conflict - in other words, use integrated Multidomain Operations (MDO) against us.

To answer that, we also have to be able to integrate our operations in order to maintain our overmatch capabilities - The MDTF is the Army's answer to operating in MDO to disrupt the adversary and maintain our advantage during the spectrum of conflict. I could go into how a MDTF fits into it during the competition, crisis and conflict phases, but it might be easier if you read the Chief's paper* on it.

Like all tasks forces, the organization is structured to the mission. The MDTF is a theater level asset, but each will have to address detainee operations to one degree or another as they can have a significant impact during all three phases.

Now, specific to your question - anything is pure speculation (it's on par with, "I was just assigned to USAEUR - what would a 31E do in a unit like this?"), but I can easily see you working in plans and operations to lend expertise about detainee operations and how they could affect, or be affected, in MDO.

The TRADOC G-2 published a short paper* that discusses how the evolving operating environment will do that - suggest you give it a read.
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* Army Chief of Staff Paper #1 (Army Multi-Domain Transformation) - https://api.army.mil/e2/c/downloads/2021/03/23/eeac3d01/20210319-csa-paper-1-signed-print-version.pdf
* Detainee Operations (A planning framework) - https://community.apan.org/wg/tradoc-g2/operational-environment-and-threat-analysis-directorate/m/documents/325704/download

You're gonna need a COL or higher from the Pentagon to explain this one. I looked this up and what I found was:

March 16, 2021 the Army describes the MultiDomain Task Force (MDTF) as “theater-level maneuver elements designed to synchronize precision effects and precision fires in all domains against adversary anti-access/area denial (A2/AD) networks in all domains, enabling joint forces to execute their operational plan (OPLAN)-directed roles"

That read like stereo instructions written in Sanskrit.

As a 31E in this unit, your role could vary based on what needs to get done out there. Flexibility is key, so be ready for anything.