In the chumash, any sources. What is the literal translation and does it mean, mot = this world, yumat = the next world?
The simple answer to your question (aside from confusing transliteration) is that it's stylistic - it's a translation meaning "he shall surely die". That's it.
As for why the emphasis, this article addresses the distinction between the usual formula (above) and the rarer formula dropping the first word. One answer given is:
The Meshekh Chokhma on Vayakhel points out that usually the death penalty is written "mot yumat," which is, in fact, the way it appears in Ki Tisa. In Vayakhel, the unusual form "yumat" appears. He claims that "mot yumat" refers to juridical punishment, while "yumat" means death at the hand of God. The parasha in Ki Tisa is defining chillul Shabbat for the future (as evidenced by the phrase li-doroteikhem (for your generations, meaning for all generations). However, in Vayakhel, the verse is specifically referring to not constructing the mishkan on Shabbat. Until the mishkan is completed, claims the Meshekh Chokhma, the legal system does not operate, and hence yumat at the hands of God rather than mot yumat in court.
The Torah often "doubles" a verb as in "Aser T'aser", "Pato'ach Tiftach" (both in this week's parsha, R'eh).
This is a "literary style" that is used for "emphasis" or "certainty". In your example, it means "He shall surely die" (or "Surely be put to death").
Occasionally, there is a midrash or some other explanation to the doubling.
The Literal meaning is "He shall surely die". The Halachic meaning finds significance in the doubling of the word as is interpreted in Sanhedrin 45b as if the specified form of the death penalty cannot be performed, then any other form can be done.
Regarding meaning this world and the next, on the drash level, I saw that in the Akeidas Yitzchak by Rabbi Yitzchak Ben Moshe Arama (a late Rishon). Likkutei Levi Yitzchak by Rabbi Levi Yitzchak Schneerson brings that idea as well.
regarding the 1st time its mentioned
shaarei kedusha 1:1
this is the zuhamas hanachash (the impurity the snake) injected in Chava (Eve) and in Adam, and through the evil and the impurity which he injected in them, he caused them sicknesses, afflictions, and death for their soul and body. And this is what is written "on the day you will eat from it, die you will die. (Bereishis 2:17)" [the hebrew word for death is repeated to indicate] death of the soul and death of the body.