Your watering will vary based on the time of year and the weather. We generally recommend watering with 10 gallons of water per inch of trunk diameter per watering. The frequency of the watering will vary.
Generally you will want to water when the top few inches of soil have dried. More detailed information can be found here: http://www.ext.colostate.edu/mg/Gardennotes/635.pdf

Pinion pines are very low water use plants. Once your tree is established it should require very little supplemental water. From eXtension.org

Information on Pinon's can be seen at the following video clip.

https://planttalk.colostate.edu/youtube-videos/tree-videos/#pinyon

How To tell If Pine Trees Need Water: 

Although pine trees are fairly drought tolerant, many will need to be watered if there is a lack of precipitation. Check for dry, cracked soil and dry, brown, brittle, or wilting needles. To check if your pine tree needs water, take a needle off of the tree and bend it. If it easily snaps in half, it is a good sign to water. Keep in mind that it is much easier to over watering pine trees than it is to underwater them. Over watering pine trees can create anaerobic soil conditions that do not allow sufficient oxygen exchange. It can also invite several pests and diseases, particularly fungi and oomycetes that cause root rot. Symptoms of over watering frequently mimic those of under watering.

How Often To Water Pine Trees:

Newly planted pine trees will need to be watered more frequently than established pine trees. Water your pine tree directly after planting. For the first 1-3 weeks after planting, water your pine tree every 1-2 days. Gradually reduce the frequency of watering for the next several weeks, working your way to watering just once per week for the following months. This watering schedule allows newly planted pine trees to develop strong, established root systems.

Most established pine trees will only need to be watered during extensive drought periods or when adding fertilizer to the soil. In climates where pine trees are native, precipitation usually provides enough water for these plants. It is important that established pine trees be watered in dry winters to prevent desiccation from freezing temperatures.

Pine trees growing in containers have different watering needs than those growing in the ground. Soil in containers will dry out quicker than soil in the ground. Water potted pine trees whenever the soil feels completely dry. Potted pine trees should be watered until the soil is evenly moist. Allow soil to dry out completely in between waterings. Some information taken from plantaddicts.com.

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Marvin

Newly planted trees will be watered where the root ball joins the native soil. You can build a berm of soil to hold the water. This will let the water soak into the soil. On an established tree, water around the drip line.

Best,

Marvin