Management should be your preference as Law is correlated with Legal aspects and shall not be fruitful accordingly.
Management plus Engineering is deadly combination and is most recommended, as Recruiter will prefer candidates with both skillsets for effective management.
MBa from top 25 Bschools is must if you're looking out for guaranteed job opportunities.
Post MbA, there are splendid job opportunities into Marketing, Finance, Operations, Human resources, IT, International Business, Retail, Avaition, Etc.

If you are planning to do management or law from abroad you have to appear for GMAT and LSAC/LSAT exam.

You can check the details from the given below link

GMAT

LSAT

If you are confused regarding your career option after engineering. You can refer below details-

1- Plan Out Your Further Studies by Specializing ie. M.Tech: Pursuing your further studies is another option to choose after completing your B.Tech studies. M.Tech is the next step that allows you to select your field of expertise and excel in it. Specialization in a particular field is provided to the students which later on will provide an edge during job interviews. To pursue M.Tech studies in the top engineering institutes such as IITs. NITs and CFTIs, the undergraduate students will have to attempt and qualify Graduate Aptitude Test in Engineering (GATE).

2- Shift over to the Business Side i.e., MBA:Y ou could be one of those people who feel that management knowledge will equip you better  in your chosen career path. If management and business has ever been interesting then you should consider pursuing MBA. Master’s in Business Administration (MBA) is also a largely pursued course in India and has a lot of scope. Fields such as HR, Marketing, Digital Marketing, International Relations, Sales and more are some of the well-known and preferred specializations.

3- Diploma Courses: Pursuing diploma courses is another alternative which will be available for B.Tech graduates. Courses such as embedded technology, VLSI, robotics, ethical hacking, protocol testing, machine designing and more are some specialized courses to name a few. These short term courses and diplomas are usually job oriented and will be helpful while applying for jobs in different industries.

4- Crack the Civil Service Examination: For engineering graduates, there is the IES in addition to the civil services one. If you feel that a government job will provide you with much better facilities and a safeguarded future, then start preparing for the civil service examinations.

5- Serve your country: You can join the Indian Army/Navy/Air Force or any other wing. Apply for AFCAT (Air Force Common Admission Test) which can land you up as a technical staff in the defense wing. The facilities provided for defense staff are good and the pay scale too while fulfilling your passion to serve the country.

All the Best!!

Kindly share which country you are interested in as the admission criteria varies accordingly. Also, please share if you have given any entrance test if yes then what was your GPA?

But generally, for management you will have to give GMAT and for law LSAT decent score would be required along with English proficiency test i.e. IELTS/TOEFL (whichever is required country wise).

Hope this helps!!!!