It depends on the key. Do is always the first note of the key.
In the Key of C Do=C Re=D Mi=E etc
In the Key of G Do=G Rey=A Mi=B etc
Gary
[Epiphone Les Paul Standard Plus Top Pro (2), Fender Player Stratocaster (2), Fender Player Telecaster (2), Squire CV 60's Stratocaster, Hamer Ecotone, Yamaha APX600 (2), Epiphone ES-339, GTX-100 (2), Spark 40 (2), Spark Mini.]