This is the 15th most frequent Hindi word.
इसक
The Hindi word "इसक" appears to be a typo or incorrect spelling. If you meant "इश्क" (Ishq), it means "love" or "romantic passion" in English.
Here, 'इसक' is used to describe possession ('this' book - specific book referred).
इसक किताब बहुत रोचक है।
This book is very interesting.
Here, 'इसक' signifies assistance ('its help' - refers to an external resource).
इसक मदद से मैंने समस्या हल की।
I solved the problem with its help.
In this sentence, 'इसक' refers to the subject matter being discussed (in context, 'this/specific topic').