I've found a number of posts on the Irrlicht forum on how to do this, but it doesn't seem to be working correctly.

Has anyone successfully found a collision node/triangle/point from a tap/click?

Here's my signal handler for a click:

void OnViewOverStart(VariantList *pVList)
	CL_Vec2i v2fPos = pVList->m_variant[0].GetVector2();
	LogMsg("VeiwOverStart: %x, %x", v2fPos.x, v2fPos.y);

	// convert to Irrlicht friendly struct
	irr::core::position2di mousePos(v2fPos.x, v2fPos.y);

	// get our scene manager
	scene::ISceneManager* pSceneMgr = GetIrrlichtManager()->GetScene();
	scene::ISceneCollisionManager* pCollMgr = pSceneMgr->getSceneCollisionManager();

	// get the ray from the screen point
    irr::core::line3df collRay;

	collRay = pCollMgr->getRayFromScreenCoordinates(mousePos, pSceneMgr->getActiveCamera()); // this appears to be getting unique values
	// get the collision 
	core::vector3df collPoint; 
	core::triangle3df collTriangle; 
	scene::ISceneNode* pNode = 0; 
	pNode = pCollMgr->getSceneNodeAndCollisionPointFromRay(collRay, collPoint, collTriangle); // I'm always getting null here

	if( pNode )
		LogMsg("	Selected Node: %s", pNode->getName());
		pNode = pCollMgr->getSceneNodeFromScreenCoordinatesBB(mousePos,0,true);	// but this is returning a node... ***
		if( pNode )
			LogMsg("	Selected Node: %s", pNode->getName());

	LogMsg("	Selected Point: %f, %f, %f", collPoint.X, collPoint.Y, collPoint.Z);