VAT on European clients for services sold from UAE or USA

If you clients are business clients with a VAT number, you can simple put "reverse charge on VAT" on the invoice, so you don't need to charge VAT.

Otherwise if it is to end customers you may apply the local VAT rate, I'm not sure for Dubai @Fred may be able to clarify.

As I can read the USA has different VAT rates, you need to speak with a accounting firm to figure out which VAT applies.

The combined rates generally rang range between 5.5 percent and 10 percent. Sales and use taxes are generally defined as transaction taxes which are charged on sales to retail purchasers, end users, or consumers of certain tangible personal property and specific enumerated services

VAT applies to everything you sell online if applicable. It doesn't matter how the sale is generated.