Look for stains. With a plastic-like surface, laminate cabinetry is more likely to repel potentially staining substances. Being more absorbent, wood will likely to absorb substances and become stained.
Observe the grain patterns. If there are repeating, mirrored sections, the cabinetry facing has been machined to give it a grain pattern that mimics wood.
Open a cabinet door and examine the back of the door and the inside of the cabinet. If the interior has a similar texture and the same color as the exterior, the cabinets are probably made from solid wood.
Run your hand along a surface. Laminate is typically smoother where wood has more texture. Feel and look for small dimples and scratches. Real wood is softer than laminate and is may receive impressions.
Unscrew and back out a hinge screw in the door and a hinge screw on the cabinet body. Look inside the hole. If it looks similar to packed sand, the cabinets are likely made of particle board or medium density fibreboard with wood or laminate veneer. If it looks like hardwood and grain lines are visible, it is solid wood.