Which needles do I need for brother xl 2120 sewing machine?

15x1 or 705 or Organ make of needles

Really, any good brand of sewing machine needle will work just fine. They are all interchangeable. What's important is which needle to use with which fabric:

For knits, use a ballpoint needle. The rounded point slips between the yarn and doesn't cut it. For woven fabrics, use sharps or universal needles. There are also special needles for use with blue jeans, with stretchy fabrics, leather, and for metallic threads.

Needles are sized by numbers, with the smaller numbers (like 90/11) for smaller, finer needles than the ones with higher numbers. The first number is European, so I'll just refer to the second number, but remember, the smaller the number, the finer the needle.

For light weight fabrics (like organza), use size 10 or 11 needles

For medium weight fabrics (like quilting cotton), use a 12 or 14

Size 16 and up are for upholstery fabrics.

Most of my sewing is done with 12s or 14s and universals (I don't sew much with knits).

Hope this helps!