Hi, Bill, I have checked some information for you. There is no record of surname Proznik in Slovenia neither today nor in genealogy records ( http://www.rodoslovje.com/index.php)http://www.rodoslovje.com/index.php), so it seems that this spelling evolved from Praznik in US.
Some links with information for further research could be found here: Toplišek, J. (2012) Leksikon priimkov: www.rodoslovje.com/ : Praznik – was very frequent surname in Slovenia before WW II; In 2007: 672 people held Praznik surname in Slovenia (+ 6 abroad), among Slovenian surnames is placed as 359th; 26% Praznik people live in Central Slovenia, 25% in Savinja valley with surrounding, 20% in Koroška region, 16% in South-East Slovenia, where also Velike Lašèe belong (http://www.velike-lasce.si/); 3% in Podravje, 6% along river Sava downstream of Ljubljana. This should be very old surname in Slovenia since it is known as common name or house name in Preserje near Krim and Podveža near Luèe in upper Savinja Valley
Online phone book for Slovenia: http://www.itis.si/http://www.itis.si/ Result from phone book: Proznik – no records Praznik – 222 names Prosnik – 8 names (but in other region than Velike Lašèe) Praznikar/Pražnikar – 19 names