Only Indian nationals and NRIs are eligible for CLAT test.
The foreign nationals desirous of taking admission to any course in any of the participating Law Universities may directly contact the concerned University having seats for foreign nationals and check on their eligibility.
These are the eligibility criteria and those who qualify for these and are deemed eligible can register themselves for the exam as soon as possible.
Yes, It is possible for you to pursue LLM through CLAT PG.
You just have to make sure you clear your Qualifying Degree (B.Com in your case) with 55% aggregate to be eligible for CLAT PG.
The syllabus for CLAT PG changes each year but it will be based mostly on GK & Current Affairs, Legal Aptitude, Elementary Mathematics, Constitutional Laws, etc.