The condensed formulas are written the way the lewis structure is drawn. So the $CH_3$ is connected to the next $CH_2$ which is connected to a C. This C is also connected to an Oxygen and the next C. The last C is connected to the Nitrogen.
Work Step by Step
$CH_3CH_2COCN$ is the condensed formula. As per the formula the $CH_3$ is connected to a $CH_2$. The second C (from the left is now connected to the previous C, next C and 2 Hydrogens. The third C is connected to the previous C, next C and with oxygen (with double bond). The last C is connected to a Nitrogen with a triple bond. The oxygen has 2 lone pairs and the nitrogen has one lone pair. Moreover, this arrangement completes the octets of C,N and O, and the duplet of hydrogen.