Aptitude, Engg. Maths, Digital Electronics, and Algorithms. You can study Aptitude from here: https://edurev.in/courses/5594_General-Aptitude-for-GATE-2017 and the rest of the subjects from here: https://edurev.in/courses/137_Computer-Science-Engineering-CE-For-GATE-2019

Essential Subjects to Focus on in CSE
In the field of Computer Science Engineering (CSE), several foundational subjects are crucial for building a solid understanding and skill set. Here’s a structured approach to prioritize your studies:
1. Programming Fundamentals
- Start with languages like C and Python.
- Understand basic programming constructs: variables, loops, conditionals, and functions.
- Practice problem-solving through coding challenges.
2. Data Structures and Algorithms
- Learn about arrays, linked lists, stacks, queues, trees, and graphs.
- Focus on algorithm design techniques: sorting, searching, and recursion.
- Implement data structures in code to grasp their practical applications.
3. Computer Organization and Architecture
- Study the basic components of computer systems: CPUs, memory, and I/O devices.
- Understand how data is processed and stored at a hardware level.
- Familiarize yourself with assembly language basics.
4. Operating Systems
- Learn about process management, memory management, file systems, and system calls.
- Understand concepts like concurrency, deadlocks, and scheduling algorithms.
- Explore different operating systems, focusing on Linux and Windows.
5. Database Management Systems
- Understand the principles of databases, SQL, and data modeling.
- Learn about normalization, transactions, and indexing.
- Practice designing and querying relational databases.
6. Software Engineering
- Study software development life cycles (SDLC), methodologies, and project management.
- Learn about requirement analysis, design, testing, and maintenance.
- Familiarize yourself with tools for version control and project tracking.
By concentrating on these key subjects, you'll establish a strong foundation in CSE, paving the way for more advanced topics and specializations.