ISN 2004 - ESRI:115728

WKT

VERTCS["ISN_2004", 
	DATUM["D_Islands_Network_2004", 
		SPHEROID["GRS_1980", 6378137.0, 298.257222101]], 
	PARAMETER["Vertical_Shift", 0.0], 
	PARAMETER["Direction", 1.0], 
	UNIT["Meter", 1.0]]

WKT2

VERTCRS["ISN_2004", 
	DATUM["D_Islands_Network_2004", 
		ELLIPSOID["GRS_1980", 6378137.0, 298.257222101]], 
	CS[vertical, 1], 
	AXIS["Ellipsoidal height (h)", up, 
		LENGTHUNIT["Meter", 1.0]], 
	ID["Esri", "115728"]]

Data from @esri/proj-codes

{
  "wkid": 115728,
  "latestWkid": 115728,
  "macro": "PE_VCS_ISN_2004",
  "name": "ISN_2004",
  "wkt": "VERTCS[\"ISN_2004\",DATUM[\"D_Islands_Network_2004\",SPHEROID[\"GRS_1980\",6378137.0,298.257222101]],PARAMETER[\"Vertical_Shift\",0.0],PARAMETER[\"Direction\",1.0],UNIT[\"Meter\",1.0]]",
  "wkt2": "VERTCRS[\"ISN_2004\",DATUM[\"D_Islands_Network_2004\",ELLIPSOID[\"GRS_1980\",6378137.0,298.257222101]],CS[vertical,1],AXIS[\"Ellipsoidal height (h)\",up,LENGTHUNIT[\"Meter\",1.0]],ID[\"Esri\",\"115728\"]]",
  "description": "ISN 2004",
  "authority": "Esri",
  "version": "10.4.0",
  "deprecated": "no",
  "areaname": "Iceland",
  "extent": {
    "slat": 59.96,
    "nlat": 69.59,
    "llon": -30.87,
    "rlon": -5.55
  }
}