An alkene on ozonolysis gives methanal as one of the product. Its structure is:

Ozonolysis gives methanal (HCHO) only if the alkene has a terminal $=CH_2$ group.
$C_6H_{11}-CH_2-CH=CH_2 \xrightarrow[(ii)\ Zn/H_2O]{(i)\ O_3} C_6H_{11}-CH_2-CHO + HCHO$
So the alkene is allylcyclohexane (cyclohexyl–$CH_2$–CH=$CH_2$).