The PortalSpawn Event is fired when an attempt is made to spawn a nether portal. If cancelled, the portal will not be spawned.

You will need to cast the event in the function header as this class:
crafttweaker.event.PortalSpawnEvent
You can, of course, also import the class before and use that name then.

Event interface extensions

Link to event-interface-extensions

BlockNeighborNotify Events implement the following interfaces and are able to call all of their methods/getters/setters as well:

ZenGetterTypeDescription
ZenGetter
valid
Type
bool
Description
If the size of portal is valid
ZenGetter
height
Type
int
Description
The height of portal
ZenGetter
width
Type
int
Description
The width of portal