Dear Aquil Imam,
You are aware that generally there are two types of training: Technical and Non-Technical.
While technical training deals with knowledge and skill, non-technical training largely deals with attitude/behavioral training.
It is relatively easier to assess the knowledge and skill gained. However, to assess this, it is important that the training content is analyzed thoroughly before the conduct of the training. In other words, what do you expect the training to deliver or what do you expect to improve? If this is assessed prior to the training (for example, the Quality Rating - QR, Overall Equipment Efficiency - OEE, Machine Availability - MA, Performance Efficiency - PE, On-Time Delivery - OTD, First Pass Yield - FPY, etc.) and after the training, you will be able to determine the effectiveness of the training. You should aim at making an objective assessment rather than a subjective assessment.
Non-technical training is generally assessed more subjectively, and the best person to give you the feedback will be the boss and information through the grapevine from peers.
In short, the effectiveness largely depends on the training content.
Assessing a trainer on technical grounds is easier. On the above count, if the parameters identified by you have improved, then the trainer is effective.
It requires extensive work to make a real assessment.
Regards,
M.V. Kannan