The names of Vedas are Rig, Sama,etc.. Similarly upanishads like Isha, Kena, Katha etc.. How exactly are they named the way they are? What about brahmanas, samhitas etc?
This is a broad question, but simply put, each of the Veda or Upanishad is named based on their content, main topics they deal with, the rishi who compiled it or the way they are structured. Here are a few examples… I am not a scholar by any extent, so if something is incorrect (factually, not based on opinion) I will be more than willing to correct it.
Rig Veda – it is named that way for it is a collection of verses called “Rk”s. Each “rk” is a composition/hymn in praise of a deity or figurehead.
Yajur Veda – Collection of verses that layout in great detail the manner, tools and method of worship/rituals. Derives its name probably from the root “yajus” which stands for worship, veneration or sacrifice.
Sama Veda – it is basically Rig Veda (with an exception of a few verses) set to a melody or musical meter. Derives its name from the root “sāman”, which is either melody or song.
Atharvana Veda – This one has mixed information online. It can either be “knowledge on collection of rituals” or because it was composed by two groups of rishis known as the Atharvanas and the Angirasa.
Isopanishad – derives its name from the very first verse “Isavasyam idam sarvam”. And aptly named because it deals primarily with the concept of “Isha”. Even if one considers the invocation, it deals with the nature of the "Isha".
Kena (Sanskrit: केन) literally means, depending on the object-subject context, "by what, by whom, whence, how, why, from what cause". This root of Kena, in the sense of "by whom" or "from what cause", is found the inquisitive first verse of the Kena Upanishad.
I am not sure if your question was to bring out the root of names of all the vedic scriptures. That is too wide a scope. But I believe this answer will have given a general idea behind how those names might have come about.