Subject pronouns include: I, you, he, she, it, we, and they. This passage uses some old English pronouns. "Thou" is equivalent to "you" and "thy" is equivalent to "your" (i.e. "Thou art with me," or "thy rod and thy staff").
Other pronouns found in this passage include object pronouns (me, him, her, us, them, you, it) and possessive pronouns (mine, his, hers, its, ours, yours, theirs). Often times possessive adjectives (my, your, his, her, its, our, your, their) are confused for pronouns, as well.
<em>I've put all of the subject pronouns found in Psalm 23 in bold type for you here: </em>
"The Lord is my shepherd; I shall not want. He maketh me to lie down in green pastures; he leadeth me beside the still waters. He restoreth my soul; he leadeth me in the paths of righteousness for his name's sake. Yea, though I walk through the valley of the shadow of death, I will fear no evil: for thou art with me; thy rod and thy staff they comfort me. Thou preparest a table before me in the presence of mine enemies: thou anointest my head with oil; my cup runneth over. Surely goodness and mercy shall follow me all the days of my life; and I will dwell in the house of the Lord for ever."