In Scripture, Satan speaks 3 times; once to man, once to God, and once to Jesus. Satan himself never denies the existence of God.

What Satan said to man:

Question God's Word - Gen 3:1
God's Word is a lie - Gen 3:4
God is hiding something good from you - Gen 3:5


What Satan said to and about God:

I come to heaven to accuse the righteous -Job 1:7
I question God's honor - Job 1:7
I am subject to God's power over me - Job 1:10
God blesses his people - Job 1:10
God is my superior - Job 1:12


What Satan said to Jesus:

Satisfy your carnal desires -Mat 4:3
Mock God - Mat 4:6
Give me your eternal soul - Mat 4:9