Separable does not really apply to English verbs. This expression is always two words followed by the object of "through" (for example "the book" or "the window"). Separable and inseparable verbs are more often associated with the German language than with English. For example, "aufsehen" is a separable German verb, and becomes "Er sah nicht auf" in a sentence.
There is a noun not often used, "lookthrough," but it is slang and should not be considered.