Can you tell me what courses can be pursued after completing 12th with Commerce as my cousin wants to take admission in it?

From full-time courses to diploma courses there are numerous possibilities for further studies after 12th in commerce field as it is a wide field.

Full time courses that can be pursued after 12th by Commerce-field students:

Chartered Accountancy (CA)
Bachelor of Business Administration (BBA)
B.B.M (Bachelor of Business Management)
B.Com (Banking and Insurance)
B.Com (Honors in Accounting and Finance)
B.A.
B.Com (Honors)
B.Com (Computers)
Fashion Designing.
Interior Designing.
Hotel Management
Tourism Management

Various Diploma courses which can be pursued by commerce students after 12th:

Diploma in Retail Management
Diploma in Accounting and Finance
Diploma in Human Resources
Diploma in Banking
Diploma in Infrastructure and Construction
Diploma in Marketing
Diploma in Plastic Technology
Diploma in Entrepreneurship
Diploma in Airhostess and Flight Steward
Diploma in Hotel Management

Top Institutes that provides part-time and full-time courses in various fields for Commerce students in India:

Institute of Chartered Accountants of India (ICAI)
Institute of Company Secretaries of India (ICSI)
Institute of Cost and Works Accountants (ICWA)
St. Stephen's College, New Delhi
Shri Ram College of Commerce, New Delhi
Loyola College, New Delhi
St. Xavier's College, Kolkata
Miranda House, New Delhi
Hindu College, New Delhi
St. Joseph's College, Bangalore
Hansraj College, New Delhi
Symbiosis Society's College of Arts & Commerce, Pune
Delhi College of Arts and Commerce (DCAC), New Delhi

Following are the jobs opportunities available for Commerce students after completing the above mentioned courses:

Charted Accountant
Lawyer
Interior Designer
Fashion Designer
Airhostess
Human Resource
Accountant
Investment Banker
Company Secretary
Banking Sector
Hotel Sector
Tourism Sector