Suppose I am provided with a positive is charged....and someone tells me to find which type of charge is present in it? Then how can we detect that the body is positively or negatively charged? Is there a device which can the charge?
In order to tell the sign of an object charge, you need another object with a known positive or negative charge. If you rub a piece of glass with silk, it will have a positive charge (by convention). If you rub a piece of amber with fur, it will have a negative charge (also by convention). Use whatever you have handy. Let's say you use a piece of glass rubbed with silk. If your object is repelled by the glass, then it has the same charge as the glass (positive). Otherwise, your object has a negative charge.
Well positive and negative charge are convention. What we call positive charge we could've called negative charge, and what we call negative charge we could've called positive charge. There are devices that detect charges, they use charged objects. Imagine I have a negatively charged ball. Remember that we could've called that ball positively charged, but the whole of the scientific community decided to call it negatively charged. If I bring a charge ball next to it, if it repels that charged ball is what we call negative. If it attracts then that charged ball is what we call positive. This convention goes down all the way to particles. In the end, someone just decided to say that electrons are negatively charged, and everything followed after.
A certain body may contain charges that can't be defined by use of your own eyes. Certain objects and instruments are needed in the test to determine the kind of charge a body has. Mostly use a glass rubbed against a silk marterial since it's positively charged. As statistics states; not the same charges attract but repel. If the subjected body repels the glass rod, it's positively charged: However if it's attracted, then the body is negatively charged