I know you can barely even see Daesung’s shirt in this picture, but from what I have to go on I think I might be right, here.
Daesung-only closeup version:
Look at the pink up top, the black on bottom, and the ‘NO’ of the logo. Going off of that, I think it’s this:
Phenomenon currently has a special store in the Japanese online retailer ZOZO, featuring limited edition items like this shirt. Click here for the shop and here for the limited items. Swagger, another of Big Bang’s favorite brands, also has a special store with ZOZO, located here.