There are several verses that are clearly Advaitic in nature.
As a kindled fire reduces all fuel to ashes, so, Arjuna! does the fire
of knowledge reduce all works to ashes.
Gita 4.37
Nothing exists here as purifying as knowledge. Perfected in Yoga, in
course of time, one wins it in one's own self.
Gita 4.38
[One acquires knowledge through the path of Jnana Yoga or path of knowledge which implies Advaita Vedanta. Adopting Bhakti Yoga would give us intense devotion.]
In like fashion W.D.P. Hill, a much-admired translator of the Gita
writes: "The famous founder of the Advaita school of Vedanta
philosophy, Samkara, was a brilliant scholar, gifted with one of the
acutest intellects in history. His Gita-bhasya is full of keen
argument; but not even the subtlety of a Samkara can conceal the fact
that the Advaita and the Gita systems are not at one. ..." Hill speaks
of undue emphasis on the power of knowledge. But it may be noted that
Hill refuses the force of texts like BG 4.37 and 4.38.
Introduction to the Bhagavad Gita Bhasya of Sri Sankaracharya by A.G.Krishna Warrier
At the end of many births, the man of knowledge directly reaches Me,
realizing, "Vasudeva is all". Such a magnanimous soul is extremely
rare.
Gita 7.19
Equally important and decisive is the preeminence of Jnana in the
Gita's scheme of moksha: "Nothing exists here as purifying as
knowledge, whose content is Vasudeva sarvamiti - Vasudeva is all
existence (BG 7.19). Here is Gita's style of affirming sarvam
khalvidam brahma -all this is Brahman (Chandogya Upanishad 3.14.1).
Introduction to the Bhagavad Gita Bhasya of Sri Sankaracharya by A.G.Krishna Warrier
I shall (now) set forth the knowable by grasping which one attains
immortality - the supreme Brahman without a beginning. It is said to
be neither existent nor non-existent.
Gita 13.12
[Brahman is not existent because It is not a gross material object and is not non-existent because It exists as all of us.]
His hands and feet are everywhere. His eyes, ears and mouth grasp
everything. His face is in all directions. He is the transcendent
spirit, enveloping all that exists in the world.
Gita 13.13
By His power the faculties of the senses function, but sense organs He
has none. He is the support of all things, but they do not affect Him.
He transcends Nature and its functions, but these constitute the
objects for His enjoyment.
Gita 13.14
He is within and without all beings. Though unmoving, He looks like
one moving (because He is everywhere). He is both far and near - far
to the ignorant and near to the knowing ones. Owing to subtlety, He
cannot be known like gross objects.
Gita 13.15
He, (the Brahman) whom aspirants seek to know, is the impartible
Whole, yet does He seem to dwell in all beings as if divided into
many. He is the generator and supporter of all beings, and their
devourer too.
Gita 13.16
The self-luminousness light of consciousness revealing even all that
is luminous. He is beyond the obscuration by the darkness of
ignorance. He, the light of knowledge, He, the quest of knowledge, He,
the way to whom is knowledge - in the innermost recess of all beings
is He established.
Gita 13.17
Verses like 13.12-17 leave no legitimate room for doubt on this score.
So much so that an objective scholar like Edgerton is obliged to set
down his well-considered view in the following words: "Thus through
its God the Gita seems after all to arrive at an ultimate monism."
Introduction to the Bhagavad Gita Bhasya of Sri Sankaracharya by A.G.Krishna Warrier