Font missing Characters Latin 1 Supplement. How to type them?
To write transliterated sanskrit you normally use the ABC Extended (formerly called US Extended) keyboard layout.  To activate that you go to system preferences/keyboard/input sources and use the plus and add buttons, then you select ABC Extended in the "flag" menu at the top right of the screen.

The shortcuts for making the various diacritic marks you need are given in

http://symbolcodes.tlt.psu.edu/accents/codemacext.html

macron above is option a, then the base letter.  dot below is option x, then the base letter.  acute above is option e, then the base letter.  āḥś

From information you provided in the Apple forums, I think you may be using a Non-Unicode font, in which case the ABC extended keyboard will not produce what you need.  If this is the case, I strongly recommend you switch to Unicode, which has been the standard for this kind text for a long time already.  A non-Unicode font will make your work pretty much unusable for anything other than printing on paper.