Where I can apply for a Jamaican visa ad an Omani...

According to the given facts and for clarification purposes, we would like to explain to you, 

You have to go to the embassy of  oman that you want to travel to Jamaican, and apply for a visa Jamaican, by filling the application form. Mention all information, including the purpose of the visit. Also, a reservation of the place that you will stay at once you arrive the country. Attach a copy of your passport (valid for six months). If you are a foreigner, you must attach the residence permit to be valid for at least six months, two personal photos with a white background, a bank statement active in the last six months before applying for a visa. The embassy will appoint an interview with you paying the fees.

Moreover, a clean criminal record must be attached as well, note that, the visa fees are not refunded if your visa application gets rejected