Hi,
The syllabus is given here http://apply-delhi.nielit.gov.in/PDF/NIC/syllabus_ScientistB_20170727.pdf

The exam pattern is specified by the authorities. The exam will be pen & paper based with objective questions. A total of 120 questions will be asked where 60 will be from Computer science and 60 will be generic - Logical, Analytical Reasoning Capabilities, Quantitative and Qualitative abilities and General Awareness and Aptitude. Each question carries 1 mark and negative marking of 0.25 for a wrong answer. To qualify you are required to score 50% marks if you belong to General Category, 40% for OBC and 30% for reserved categories.

For preparation, check the Computer Science Syllabus. Prepare for the given topics. As for the general section, use any of the competitve books available in the market.