I know how fish emulsion works as a foliar spray on deciduous shrubs, but will it work on needle leaved evergreens such as mugho pines and junipers? If not, what should be used for comparable result?
Foliar applications of fish emulsion, or pretty much any foliar nutrient application, is effective because the nutrients enter the plant directly through the stomata, or pores, of the leaves.
Evergreens have fewer stomata than deciduous trees but even needles contain stomata therefor foliar applications should also be effective. I couldn't find any specific research on fish emulsion and conifers but there are other studies showing foliar application of urea with positive results.
Yes it does. Just add a small amount to water and do a light mist over the leaves when it is not sunny. If it is sunny your spray will cause black spots on the leaves. The result would be leaves that are a little bit larger.
Most foliar fertilizers should be rich in micronutrients, Nitrogen(N) and Phosphorus(K). Here is a powerpoint that explains how foliar feeding works