Scissors are counted as two objects joined together, this 'scissors' or 'a pair of scissors' is correct. 'Scissors' is a plural noun. Thus "look at these scissors" is correct, "look at this scissors" is not. Although "look at this pair of scissors" is also correct.
Definition of SCISSORS (Merriam-Webster): "a cutting instrument having two blades whose cutting edges slide past each other."
Each blade in the pair is one scissor, although this usage has effectively become obsolete, which sometimes leads to some confusion in the implements having a plural name.
It is the same principle that applies to pants with each side and leg hole being a 'pant', and glasses, with a 'glass' for each eye.