Improve the bracketed part of the sentence.
"Please pass me that (scissors)."

The noun "scissors" is a plural-only noun (it has two symmetrical parts operating together). It cannot be preceded directly by a singular demonstrative pronoun like "that".
To make it countable and compatible with "that", we use the phrase "pair of scissors".

Note: "scissor" without an 's' is incorrect in standard English usage for the tool.
Therefore, "that pair of scissors" is correct.