Zdenka is from the Czech / Slovak / Croatian Zdenka — feminine of Zdeněk — from the Latin Sidonius (from Sidon) via Slavic phonological adaptation. Zdenka is one of the Czech feminine names.
Zdenka does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Zdenka reduce to 7, The Seeker. This is a traditional interpretive system, not a factual claim about the name.