How can I specify pyridine as a substituent?
The issue, I think, is to specify how the pyridine is connected. This means you have to identify which carbon on the pyridine ring is connected. This picture shows the numbering:



So, using your example the structure and names of the various possibilities would be (using connections on the 3-position of the benzonitrile ring as an example):



I'm sure you can generalise from this example.