What is the correct pronunciation of Czechia ?
CZECHIA is pronounced correctly /ˈtʃɛkiə/, written by symbols of the IPA (International Phonetic Alphabet), in simple transcription "checki-ya".
The word comes from the root "Czech" (adjective, language, inhabitant), which is pronounced /ˈtʃɛk -/ (IPA), simply "check" and originally Latin suffix "-ia".
Notice: There is a tendency to read the word as "chechiya", although it would seem to be obvious that one who can pronounce "Czech" correctly will also be able to read Czechia.....
"Cz": The digraph "cz" comes from the old Czech orthography, typical for West Slavic languages (Czech, Polish), which was taken over by Latin and later also by English for the name to express pronunciation of /t͡ʃ/ (IPA key). In Polish is "cz" digraph still used, in modern Czech (since the standardization of modern orthography in 19th century) is substituted by consonant "č" (however it was introduced already at the break of 14th and 15th century), usually denoting the voiceless postalveolar affricate consonant [t͡ʃ] like the English "ch" in the word chocolate. "Č" originated in Czech language, and from it was adopted in Slovak, Croatian, Macedonian, Slovenian, Bosnian, and Montenegrin. It is used also in Latvian and Lithuanian.
P.S. It is necessary to mention, that English Wikipedia wrongly says (and rejects correction /!!/), that “cz” in English came from Polish at the end of 18th century (without any source), which is a nonsense, because in Latin is “cz” documented already in 16th century (e.g. “Czechia” from 1569 in the Latin preface to the "Musica" of Jan Blahoslav) and this digraph in various forms (adjectives, nationality, name of the country) is very frequent in Latin texts in Baroque period. The fact that the spelling of "Cz" in the word Czech does not come from Polish is further supported by its first recorded use in English in the word “Czechians” by Peter Heylyn in 1625 in his “Mikrokosmos: A little description of the great world. Augmented and reuised.” (2nd edition) on page 298:
Peter Heylyn is explicitly referencing Czech sources, including Jan Dubravius.This clearly shows that the word “Czech” does not come from Polish in the 19th century, which is a myth.