All the graph editing support is editor only, using all of the editor infrastructure in UE, and thus can’t be compiled into a shipping game (unless, perhaps, you come to an expensive arrangement with EPIC? Anything’s possible with enough zeros on a check.)
You will thus have to, essentially, implement your own GUI drawing program, using the Unreal UI features that are available. If I were to do it, I’d probably just build one fat widget in C++ that “did the thing” and write the box-drawing, spline-drawing, mouse-tracking stuff all in C++, although I’d still need to expose parts of it all to Unreal reflection, so the game can know which nodes are where and which node inputs/outputs are connected.
If you’ve done GUI development before, in C++, it’d probably be a week or two to get really used to the UE/slate way of doing GUI, and then a couple of months to build a good graph editor foundation for a game to use (somewhat dependent on feature amount – a few weeks for “move boxes around and draw lines between pre-defined slots,” and a lot more for “slots can come and go, users can rename things, there are custom icons, text, and other presentation in the boxes, and it’s all reflected out to the game as it happens.”
THEN you will realize that your players probably also want some way to debug all this, inspect data as it flows through the graph, and so on – you’d want to actually “execute” this graph, with introspection, and that’s a whole other kettle, which is just as big …