how hard does a 1997 Dodge Dakota have to be hit from the passenger side to cause the airbags to deploy?

There is no direct answer to your question. In most cases manufacturers, Dodge included, have gone to a combination of front bumper impact sensors, and internal G-force sensors which detect forces exerted on occupants in a crash. While it might be safe to assume a 35mph t-bone collision should set the airbags off, a lot of variables come into play which may mean that they may or may not be deployed in such a case.