When should I say Takbeer (saying: "Allahu Akbar") while getting up after an odd Rak‘ah (unit of prayer) for the next Rak‘ah? Should I say it before Jalsatul-Istiraahah or after it?

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger. {C}

If you sit for Jilsatul-Istiraahah (after the first or third Rak‘ah), then you say the Takbeer during Jilsatul-Istiraahah, and then you stand up without saying Takbeer. Ibn Qudaamah said:

"It is recommended to start the Takbeer while starting to raise one's head from prostration and to end the Takbeer when he stands up straight (i.e. when he is completely in the standing position) so that the Takbeer would cover all of the transition stage [from prostration to the standing position], which is the pillar during which it is legislated to say the Takbeer. The same applies to all Takbeers with the exception of the one who sits for Jilsatul-Istiraahah, as his Takbeer ends when his sitting ends, and then he stands up without saying Takbeer.”

Allah knows best.