The MoveBlock, DSNewPtr, DSDisposePtr and other memory functions can be found in the special LabVIEW library path in NXG, same as with LabVIEW 20xx. Create a Shared Library Interface, set its path to LabVIEW, then add each of the functions:
The available function symbols won't auto-populate like they do in LabVIEW's Call Library Function Node, but they are there. Also NXG (annoyingly) lacks the Adapt to Type input parameter, so you may need to create multiple definitions of MoveBlock if you're using multiple types.
I find it quicker to create the function prototypes in LabVIEW using CLFNs, then import it into NXG. Here are links to code snippets of the above function definitions which can be imported into NXG.