There are several online forums and communities where you can discuss doubts or queries related to your optional subject for the UPSC exam. One such platform is EduRev, which is an online learning community that offers a wide range of resources for UPSC aspirants. Here are the details of how you can use EduRev for discussing your doubts and queries:

1. EduRev Community:
EduRev has a dedicated community section where you can post your doubts or queries related to your optional subject. You can create a new post and ask your question, and other community members, including fellow aspirants and experts, can provide answers and solutions. This is a great way to engage with like-minded individuals and get different perspectives on your doubts.

2. Subject-specific Groups:
EduRev also has subject-specific groups where you can join a community of aspirants who are preparing for the same optional subject as you. These groups have discussions, study materials, and practice questions related to the subject. By joining these groups, you can interact with fellow aspirants who have similar doubts and queries.

3. Live Doubt-Solving Sessions:
EduRev frequently conducts live doubt-solving sessions where you can ask your doubts directly to subject experts. These sessions are conducted in a webinar format, allowing you to interact with the experts in real-time and get immediate answers to your queries. The experts provide detailed explanations and clarify any doubts you may have.

4. Question and Answer Section:
EduRev has a dedicated question and answer section where you can browse through previously asked questions and their answers. This section is organized by subject and topic, making it easy to find relevant information. If your doubt or query has already been asked, you can find the answer here without having to post a new question.

5. Discussion Forums:
Apart from EduRev, there are other online forums and communities where you can discuss doubts and queries related to your optional subject. Some popular platforms include UPSC Forum, Quora, and Reddit. These platforms have dedicated sections for UPSC aspirants where you can ask questions, participate in discussions, and get answers from fellow aspirants and experts.

In conclusion, EduRev is a reliable and comprehensive platform where you can discuss doubts and queries related to your optional subject for the UPSC exam. It offers a variety of features such as community discussions, subject-specific groups, live doubt-solving sessions, and a question and answer section to cater to your needs.