How many brachos does one have to make up on yom kippur in order to make the 100?
According to the simple count, a person has to make up 35 berachos on Yom Kippur (depends on how we calculate birkas ha-Torah, and depends on the berachah of she-asah li kol tzarchi).
The way we make them up is by means of the berachos of kerias ha-Torah and haftarah. On a weekday, this comes to 30 berachos (one should have careful intention to answer amen).
The Mishnah Berurah (46:14) cites from the Magen Avraham that the rest can be made up by smelling and making a berachah of minei besamim. Some authorities object to making birchos ha-re’ach on Yom Kippur, and prefer to complete the total with asher yatzar. The Mishnah Berurah adds that where nothing else works, one can rely on the berachos of chazaras ha-shatz.
This issue is complex, and involves a number of different opinions and possibilities; we will bli neder dedicate a full-length article on the subject in the future.