Cofactor required for lipoprotein lipase activity is:
The enzyme lipoprotein lipase is present in the capillary walls of adipose tissue, cardiac and skeletal muscle, besides other tissues. 
lt hydrolyses a portion of triacylglycerols present in chylomicrons and VLDL to liberate free fatty acids and glycerol.
Lipoprotein lipase is activated by apo C ll.

Key Concept:
Lipoprotein lipase is activated by apo C ll.
Ref : Textbook of Biochemistry, Satyanarayana
Apo A-II
Apo C-II
Apo C-III
Apo B-II