what will i write to a letter???

i think your professor wants you to get external experience which could be beneficial for your own growth. aside from that, maybe one of the requirements in the OJT is the performance evaluation or application of your learned knowledge. if you will have your OJT in your own company, and you will be doing the performance evaluation for yourself, then i think it's biased and subjective, not objective. but if you still want to push thru with the idea to do OJT in your own shop, you can say: "dear sir, i'm writing this in connection with my request to do the on-the-job-training at *(the name of your shop/company) under the supervision of **(name of in charge. it must not be you.) due to ***(create valid reasons why. it could be because of proximity to school/home; opportunities available; hands-on training/troubleshooting; compensation/pay/salary. then include the benefits like: ease, accessibility, job is course-related etc). on-the-job-training programs are geered to enhance students' capacity and improve our growth potential so that we may be prepared to do the tasks and responsibilities required of us in our future jobs after graduation. i believe that i can get this thru the OJT at *(the name of your shop/company). thank you. i trust that you would give consideration to this request. have a good day! respectfully, (your name)" ---------------------- hope this could be of help. goodluck! :)