Doesn't he work for your company during the training period? Naturally, he should be put to work. Then why this question?
Apprentice from the RI Centre or Optional Trade
Is he an apprentice from the RI Centre or under Optional Trade? Then he should be paid a stipend fixed by the Central Government.
Engagement as per Standing Orders
Is he engaged following the clause in the Standing Orders of your company? Then pay him the required amount as per Standing Orders. It shall not be less than 75% of the statutory minimum wages fixed by the government for his category of work.
Payment for Trainees Outside the Above Categories
If he does not belong to the above categories, pay him a "salary" not less than the statutory minimum wages fixed by the government. A trainee other than the two mentioned above is at par with any other employee of your company. The only difference is that he may not be that skilled and therefore, you can treat him as either semi-skilled or even unskilled. But in no way can he be employed without being paid a salary and without receiving ESI, PF, Bonus, etc.