First, be certain what you are looking at in the print copy. The letter you have copied looks like the alternative print form of the Greek letter theta, not a script regular theta. Does the print copy call it a script letter?
A table of the alternative forms of Greek letters is on page 34 of "An Introduction to Braille Mathematics." I have attached a photo of that table. The braille transcription of the alternative theta is (46, 4, 1456)
If you determine that the letter is truly a script regular theta, it is brailled as follows: (4, 46, 1456) The script indicator (dot 4) is brailled first, followed (unspaced) by the Greek letter indicator (dots 46), followed (unspaced) by the letter (theta, dots 1456).
See Nemeth Code Rules IV and V, and Appendix A (page 208).
Thank you, Lindy, for your quick, informative response. The print copy (University Physics with modern Physics, Bauer & Westfall, page 266) does call this symbol "script theta." Thank you for so clearly covering both possibilities! Karen