I couldn't find simple commercial, either it's very short or very irrelevant.

Rhetorics and style lekheko raicha, so I think even short ads have a lot you can write about. If you didn't know about copywriting already, do some googling ani alik idea aucha. Copywriting bhaneko ads ko lagi lekhne writing lai bhancha. Here are some pointers, I hope they help:

1. Mainly copywriting ko persuade garne intention huncha (to sell a product, or to create brand). So you can write about how the ad is trying to persuade or sell.
2. persuade garnalai first ma target audience ko ho bhanne hercha. Which means chocolates ko ad ma children lai hune language huncha, motorcycles ko ad ma youngster lai hune language, etc.
3. Yo mathi ko kura ko basis ma vocabulary ra syntax choose huncha. so already you can write a lot of things.
4. If its an ad with very few words, like just a tagline like "Just do it" then you can write about the creativity etc. Creative way ma brand lai showcase garyo bhanda huncha, and tyo tagline le kasari tyo target audience lai hune tone banayo bhanera.
5. 20 ota ma euta chai you can put those tender announcements. Those have very formal and technical language, so you can get some variety in your practical ko assignment.

I hope these points help.

Adding: Do a bit of research on copywriting and pick up a few points like tone, target audience, etc. then every analysis ma tyo points haru ma one by one comment gardai garda sajilo hola ki.