Here's how to tell:
* Short vowel sounds are usually found in words with one syllable and a single vowel.
* Long vowel sounds are often found in words with two vowels, a silent "e" at the end, or a vowel combination (like "ai", "ee", "oa", etc.).
Since "poke" has only one syllable and one vowel, it has the short vowel sound of "o" as in "hot" or "box".