Haven't researched it but were Biblical Jews baptized before John the Baptist came baptizing? If so, what verses can I read that?

JW's refer to John as the Baptist, the Baptizer or even just as John.

See if this helps:
MATTHEW
Study Notes—Chapter 3
3:1

the Baptist: Or “the Immerser; the Dipper”; referred to as “the Baptizer” at Mr 1:4; 6:14, 24. Evidently used as a sort of surname, indicating that baptizing by immersing in water was distinctive of John. The Jewish historian Flavius Josephus wrote of “John, surnamed the Baptist.”


MARK
Study Notes—Chapter 1

1:4
the Baptizer: Or “the Immerser; the Dipper.” The Greek participle rendered “Baptizer” here and at Mr 6:14, 24 could also be rendered “one who baptizes.” The form is slightly different from the Greek noun Ba·pti·stesʹ, which is rendered “Baptist” at Mr 6:25; 8:28 and in Matthew and Luke. The two designations, “Baptizer” and “Baptist,” are used interchangeably at Mr 6:24, 25.—See study note on Mt 3:1.


JOHN
Study Notes—Chapter 1

John: That is, John the Baptist. The writer of this Gospel, the apostle John, refers to John the Baptist 19 times but, unlike the other Gospel writers, never uses the designation “the Baptist” or “the Baptizer.” (See study notes on Mt 3:1; Mr 1:4.) The apostle John does distinguish between the three Marys. (Joh 11:1, 2; 19:25; 20:1) However, he did not need to make such a distinction when referring to John the Baptist, since the apostle never refers to himself by name and no one would misunderstand which John was meant. This is another confirmation that the apostle John wrote this Gospel.—See “Introduction to John” and study note on John Title.




https://www.blueletterbible.org/esv/mar/6/1/t_bibles_963014Mark 6:14 (ESV) King Herod heard of it, for Jesus’[fn] name had become known. Some[fn] said, “John the Baptist[fn] has been raised from the dead. That is why these miraculous powers are at work in him.”

“John the Baptist[fn]  Greek baptizer; also verse 24

6, 7. (a) Explain the significance of John’s baptism. (b) What unique baptism did John perform?

⁶ We first read of baptism in the Bible in reference to that performed by John the Baptist. (Matt. 3:1-6) Those submitting to John’s baptism did so as evidence of their repentance over sins against the Mosaic Law. It is noteworthy, however, that the most important baptism that John performed had nothing to do with repentance. John had the unique privilege of baptizing Jesus, the perfect human Son of God. (Matt. 3:13-17) Jesus was without sin, so he did not need to repent. (1 Pet. 2:22) His baptism symbolized the presenting of himself to do God’s will.—Heb. 10:7.

⁷ During the course of Jesus’ earthly ministry, his disciples also performed baptisms. (John 3:22; 4:1, 2) Like those performed by John, these baptisms symbolized the individuals’ repentance over sins against the Mosaic Law. However, after Jesus’ death and resurrection, baptism would take on a much different meaning for his followers.


https://wol.jw.org/en/wol/d/r1/lp-e/1102014615?q=jesus+baptism+sins+john&p=par