The places in the Bible where Jesus commanded this work be done by door to door means are:
Matthew 10:11And into whatsoever city or town ye shall enter, enquire who in it is worthy; and there abide till ye go thence.
12And when ye come into an house, salute it.
13And if the house be worthy, let your peace come upon it: but if it be not worthy, let your peace return to you.
14And whosoever shall not receive you, nor hear your words, when ye depart out of that house or city, shake off the dust of your feet.
40He that receiveth you receiveth me, and he that receiveth me receiveth him that sent me.
41He that receiveth a prophet in the name of a prophet shall receive a prophet's reward; and he that receiveth a righteous man in the name of a righteous man shall receive a righteous man's reward.
Luke 94And whatsoever house ye enter into, there abide, and thence depart.
5And whosoever will not receive you, when ye go out of that city, shake off the very dust from your feet for a testimony against them.
6And they departed, and went through the towns, preaching the gospel, and healing every where.
Acts 20:20, 21
20And how I kept back nothing that was profitable unto you, but have shewed you, and have taught you publicly, and from house to house,
21Testifying both to the Jews, and also to the Greeks, repentance toward God, and faith toward our Lord Jesus Christ.
42And daily in the temple, and in every house, they ceased not to teach and preach Jesus Christ.
Acts 2:46And they, continuing daily with one accord in the temple, and breaking bread from house to house, did eat their meat with gladness and singleness of heart,
47Praising God, and having favour with all the people. And the Lord added to the church daily such as should be saved.
Rev. 3:19, 20
19As many as I love, I rebuke and chasten: be zealous therefore, and repent.
20Behold, I stand at the door, and knock: if any man hear my voice, and open the door, I will come in to him, and will sup with him, and he with me.
Jesus is not personally knocking on all doors, but he did command his followers to do it and to do it all the days until the end of the system of things. Matthew 28:18-20, Acts 1:8......Matthew 24:14.
It doesn't make money and is beneath the dignity of most preachers to do this work. Even most of the door to door religions only ask people to do it briefly if they want to be leaders, or to get baptized or to do a specific short time of service like 2 years. For us, our service to God is all our lives.
We KNOW you cannot earn salvation. That is not why we do it. Eph. 2:8, 9 has the same content in NWT as all other Bibles.
But it is a command and God only gives eternal life to those who obey his commands. Hebrews 5:8, 9, Matthew 5:19, 20, 2. Cor. 5:15, Philip. 1:29, more.
KJV from Bible Gateway used for cut/paste.