What is the biblical basis for the belief by Seventh-day Adventists that evangelized Gentiles should keep the Sabbath? Which passages of Scripture are canonically or typically cited by Seventh-day Adventists in defense of the belief that evangelized Gentiles are to keep the Sabbath (sunset Friday to sunset Saturday) the same as the Jews in the Old Covenant? How do they normally interpret those passages in order to come to that conclusion?
Traditionally, Seventh-day Adventists hold that the Ten Commandments (including the fourth commandment concerning the sabbath) are part of the moral law of God, not abrogated by the teachings of Jesus Christ, which apply equally to Christians.
Following are excerpts from the Seventh-day Adventist Church regarding Sabbath:

The gracious Creator, after the six days of Creation, rested on the seventh day and instituted the Sabbath for all people as a memorial of Creation. The fourth commandment of God’s unchangeable law requires the observance of this seventh-day Sabbath as the day of rest, worship, and ministry in harmony with the teaching and practice of Jesus, the Lord of the Sabbath. The Sabbath is a day of delightful communion with God and one another. It is a symbol of our redemption in Christ, a sign of our sanctification, a token of our allegiance, and a foretaste of our eternal future in God’s kingdom. The Sabbath is God’s perpetual sign of His eternal covenant between Him and His people. Joyful observance of this holy time from evening to evening, sunset to sunset, is a celebration of God’s creative and redemptive acts. (Gen. 2:1-3; Exod. 20:8-11; 31:13-17; Lev. 23:32; Deut. 5:12-15; Isa. 56:5, 6; 58:13, 14; Ezek. 20:12, 20; Matt. 12:1-12; Mark 1:32; Luke 4:16; Heb. 4:1-11.)

Adventists believe that the formal giving of the Law to Israel does not indicate that Israel alone is morally responsible before God for the things represented in the law:

The great principles of God’s law are embodied in the Ten Commandments
and exemplified in the life of Christ. They express God’s love, will,
and purposes concerning human conduct and relationships and are
binding upon all people in every age.

The basis of Adventist belief that the 4th commandment applies to all people in every age is that the Sabbath is first described in the creation account wherein God Himself rested.  This Sabbath memorial of what God has done in creation is embodied in the Law and exemplified in Christ and, by extension, the Church (Christ's body, Christ's bride, God's people):

the Lord made “the heavens and the earth, the sea, and all that is in them” and rested on the seventh day. Thus He established the Sabbath as a perpetual memorial of the work He performed and completed during six literal days

It appears that, rather than making a distinction between the universal moral law and the Ten Commandments given to Israel through Moses, SDA holds them to be one and the same.  The following excerpts are taken from the doctrine section of an SDA apologetic s website.

Seventh-day Adventists are in full accord ... that the moral
law is eternal in its very nature and has not been abrogated. We
believe that these eternal moral principles are unchanged and
unchangeable. We further believe that these basic principles are found
in the Decalogue—Ten Commandments, or the moral law.


Some think of the Sabbath as an institution related only to the Hebrews. Those who press this point claim that the Deuteronomy version of the Decalogue emphasizes that the Sabbath was given exclusively to the Hebrews, because they had been delivered from slavery.
The silence of the latter part of Genesis regarding the Sabbath is
understandable when one remembers that acquaintance of the patriarchs
with God's commandments was taken for granted. The author of the
historical record in Genesis did not deem it necessary to mention it
in his sweeping survey of the centuries. But Abraham kept the
commandments of God (Gen. 26:5)—the Hebrew word here used for
&quot;commandments&quot; being the same as that used for the Decalogue in
Deuteronomy 5:10, 29. Kalisch mentions this as the law written in the
heart of man, and the Pulpit Commentary states that the word means
&quot;that which is graven on tables.&quot; Abraham acknowledged and obeyed the
moral law of God. If so, would that not include the Sabbath? The
Companion Bible (Gen. 26:5) says Abraham had a charge, to be observed;
commandments, to be obeyed; statutes (decrees), to be acknowledged;
and laws &quot;instruction,&quot; the Torah), to be followed.
And during their wilderness experience, God tested His ancient people
as to whether they would walk in the way of His commandments (Ex.
16:4). The test came on the subject of the Sabbath. And comparison of
Exodus 16:1 with Exodus 19:1 shows that this occurred several weeks
before the promulgation of the Decalogue. They must, therefore, have
known not only of God's law but also of specific commandments embraced
therein, as evidenced by this reference to the Sabbath.