What kind of questions are asked in interviews for M. Tech. program admission at IISC?

Then you are asked to walk towards the board and take a chalk piece. You may be asked the subjects of your choice and questions are mostly from that particular subjects.

I haven't attended the M Tech interviews but attended the MS interview for CSA and SERC Departments at IISC. So, My answer may be of some help. Moreover, the Branch is not mentioned in the question and my answer would basically relate to CS department.

What they look for
1) Strong hold on basics in the subjects studied in graduation course.
2) Minimum insights on the subjects you choose for your post graduation.
3) If your mode of entry was through competitive exams like GATE, the way you answer their first few questions will indirectly help them determine if you have come from coaching institutes or by self study. The prefer the latter but, it surely is not the end of the road for the former provided you are good with the concepts.

Any department has a written test followed by a round of interview. The interview process happens in slots(two slots a day for a few days) and each slot generally has 20-25 students attempting. First you are given a form and asked to fill your choice of subjects or labs for your PG course. You need to choose judiciously as your interview depends on it.

Written test
Written test generally comprises of very few questions (10 were asked in CSA and 7 in SERC) with a time duration of 30 minutes. The questions are from basic maths and few of the core subjects.
In CSA, questions were from combinatorics, Probability(poissons distribution) and basic questions from core subjects like Operating systems(theoritical question about pipelining), Compilers(finding all possible strings from a given grammer) etc. Some questions were given about filling the blanks with appropriate code in C to implement a particular logic.
SERC written test had mostly mathematics(Engineering mathematics too) with just two questions on coding(again fill in the blank type) a question on limits and co-ordinate geometry were also asked.
The questions may be of multiple choice type, fill in the missing blanks type and most of them short answer type. There will be space for rough work and even your rough work carries mark. One has to attempt all questions to stand a chance for interview. The level of complexity is similar to that of 1 mark questions in GATE exam. Also, CSA department called almost everyone for interview after the written test while SERC shortlisted only 8 out of 25 odd candidates who gave the written test.

Interview
The size of interview panel depends on department. CSA had multiple panels for different subjects the students select, while SERC had a single panel with ten professors.
They first read out your profile to make you feel comfortable. Then you are asked to walk towards the board and take a chalk piece. You may be asked the subjects of your choice and questions are mostly from that particular subjects. CSA department emphasized more on mathematics. Students were asked to derive various equations on board and most questions were definition based fom relations, functions, sets and probability.
SERC professors ask to write pseudo code on board. They were quiet helpful and guide you provided you show some progress and keep talking when you get struck somewhere.
Lastly, You know that you stand a chance to be selected if you are asked questions from Advanced subjects after answering the basic subjects and your interview happens for approximately 40 minutes to one hour.