In the word 'सांस्कृतिक' (cultural), the suffix is—

The word 'सांस्कृतिक' is derived from the root word 'संस्कृति' (culture) by adding the suffix 'इक' (ik), which transforms a noun into an adjective. The vowel change (संस्कृति → सांस्कृतिक) follows the rule of vṛddhi when 'इक' pratyaya is added. This is the same pattern as धर्म → धार्मिक, समाज → सामाजिक, इतिहास → ऐतिहासिक. The suffix is 'इक'.