Line 144 is filled from the T5007 and relates to WCB benefits. If you are using the online version, you do not have access to a return form, but you can check information by going to review>bottom line summary and scroll down to detailed tax summary.
http://www.cra-arc.gc.ca/tx/ndvdls/tpcs/ncm-tx/rtrn/cmpltng/rprtng-ncm/lns101-170/144-eng.html