Thanks for writing. The best time to prune dogwood is right after it finishes blooming. To help your dogwood along, I'd amend the soil with organic matter, such as compost. That should help it a great deal.
As far as why it hasn't bloomed, that could be because of a number of factors. Dogwoods produce their flowerbuds the year before they bloom, and since you're in Zone 5, which can be marginal for dogwoods, you can lose some or all of the flowers to winter damage or a late spring frost.
Be sure to keep your dogwood well watered so the soil is moist, but not wet. Dogwoods don't hold up well to drought, especially when they're in full sun.
--Justin, Senior Garden Editor, BHG.com "