Smoke screen on unit with gear +2 unit got 4 might what is the result

1 might.

Smoke Screen (-4 might, to a minimum of 1) snapshots at resolution: with the unit sitting at 4 (base + 2 from the attached gear), the effect remembers a -3 reduction, giving 1. Rule 477.3.b.

The gear still contributes its +2 as a continuous Might Bonus while attached, so the math is 2 + 2 - 3 = 1. If that gear later leaves (unit dies, Equipment recalled, etc.), the snapshotted -3 remains for the turn and the unit would drop to -1, treated as 0 (Rule 143.2.b).