I use 18-140 Nikkor . This lens have two A & M focus mode and this lens is AF-S that mean when auto focus is enable the focus ring dose't move. If i do manual focus when the lens is at A mode , does it harm the lens ? or its safe.
In general, you can damage your lens if you turn the focus ring while in autofocus mode. The exception is ring-type lens motors, which are often branded "ultrasonic" or similar. (Nikon uses "Silent Wave Motor", although it unhelpfully uses this designation for both ring and "micromotor" designes). There are also some Pentax lenses which have a clutch mechanism.
Assuming that this 18-140mm is your lens, note that it's explicitly listed as having "full-time manual focus override". This means that it either has a ring-type motor, or a clutch mechanism, so it should be safe.
In User-Guide it's explained well : A Mode : Auto focus (Manual Focus * ) available only when single-servo AF ( AF-S ) is selected as the camera focus mode ( So its safe when mode set to A and in settings focus mode set to AF-S ) so i've got my answer with Lens user-guide manual .