1. Eikon is an end user product. Eikon customer is licenced to utilize any data retrieved from Eikon for user's individual use only. Eikon provides access to a wide variety of Thomson Reuters data assets including streaming market data, news, fundamental and reference data etc. etc. Elektron is the platform currently used primarily for distributing streaming market data. It provides streaming market data to Eikon and it can also be accessed through a number of enterprise datafeed products, which allow clients to consume streaming market data in enterprise applications. You can think of Eikon as a market data terminal and of Elektron as a datafeed providing streaming market data.

2. TRKD is a service providing access to a wide variety of Thomson Reuters data assets primarily for use in Web portals. This service may come with a license to redistribute Thomson Reuters data externally, i.e. to users outside of the client's organization.
3. TREP is a set of middleware components providing capabilities to manage the distribution of streaming market data within client's organization.
4. See
http://financial.thomsonreuters.com/en/products/data-analytics/market-data/velocity-analytics-market-data-analysis.html
5. TR provides a variety of products for numerous use cases. There's no one preferred language. The choice of language depends on a number of factors the most important one being the use case. For many use cases we offer APIs in multiple languages. Where appropriate we also offer a number of language agnostic REST and Websockets APIs.
6. Most TR APIs are tied to a subscription product. The APIs are free, but in order to retrieve data using these APIs you need to subscribe to a service, which is not free.
7. Thomson Reuters is a platform company. We strongly believe in and encourage partnerships. Please visit our Partner Marketplace for more details.