Did you mean "Who to interview" or "how to interview"?

If "Who", then I suggest you look up the names of some dog
behaviouralists (probably listed under training) in your local yellow
pages. They will have lots of experience in differnet types of dog
behaviours, what is normal and what is unusual.

If "How", then I suggest you begin with some traditional research (i.e.
books), from there you can develop some questions, such as "When a dog
notices another in it's territory does it usually bark, growl or run
away?" You could then go to a park, or walk down a street with a dog
and notice what happens when two dogs come near each other. Keep a log
of what happens each time, then go home and analyse your results.

You should be able to make some conclusions such as:
20% of dogs bark on first encounter
80% growl on first encounter

IMPORTANT - dogs are sensitive about home territory and there is a risk
that they will become aggressive. Be careful.

Hope this helps,

Tara