There’s no J in Hebrew period! The fact is the old Hebrew language had no vowels that’s why they switched to Aromaic. Vowel points were introduced in the 10 century AD. There’s very little evidence that anyone spoke or wrote Hebrew back in the days previous to the 6th century BC .
The oldest Torah is only 600 years old the oldest manuscripts that could be called the Old Testament are the original Greek Septuagint which was originally only the first 5 books.
Any older manuscripts of Old Testament writtings in Hebrew then the Septuagint were just small fragments of wisdom sayings. Oldest manuscripts of gods name and stories and descriptions of the biblical god are found at Ugarit. His name is El and the stories written their were later used as foundation for some of the stories we read today in the Old Testament.