Assalamualaikum w.b.t. I have a question. Are non-Muslims considered as najis since they’d touch najis in their daily lives such as swine, dogs and others? Hope for an answer.
Waalaikumussalam wrt. wbt.,
Alhamdulillah, praise and gratitude to Allah SWT for His countless blessings for us all. Praise and salutations to our beloved Prophet Muhammad PBUH, his family, companions, and all those who follow his footsteps until the Final day.
We begin with the statement of Allah SWT:
إِنَّ اللَّهَ يُحِبُّ التَّوَّابِينَ وَيُحِبُّ الْمُتَطَهِّرِينَ
“Indeed, Allah loves those who are constantly repentant and loves those who purify themselves.” 
This means that Allah SWT loves those who are clean from filth and hadas, whether it is physical or spiritual filth. 
Non-Muslims are not najis
Some scholars in madhhab Zahiri are of the opinion that non-Muslims are considered as najis in terms of its ‘ain (matter) and they argued that this matter is based on the statement of Allah SWT:
يَا أَيُّهَا الَّذِينَ آمَنُوا إِنَّمَا الْمُشْرِكُونَ نَجَسٌ فَلَا يَقْرَبُوا الْمَسْجِدَ الْحَرَامَ بَعْدَ عَامِهِمْ هَٰذَا
“O you who have believed, indeed the polytheists are unclean, so let them not approach al-Masjid al-Haram after this, their [final] year.” 
Then, the majority of scholars answered this opinion saying, unclean in this verse means filth and uncleanliness in terms of their faith of non-Muslims that should be avoided and not their bodies. They argued that Islam sanctions that marrying the People of the Book is permissible and if their sweat is najis, then surely their husbands wouldn’t be safe from these najis. The majority of scholars also answered that the Prophet PBUH once performed ablution using the container of the polytheists, tied a polytheist captive in a mosque and ate cheese from the Catholic country and ate a lamb dish a gift from a Jew. 
Likewise, Syeikh al-Islam Zakaria al-Ansari stated that humans are honoured. This honour implies that they aren’t ruled as najis even after their death, regardless of whether they are Muslims or non-Muslims. While unclean meant in verse 28 in Surah al-Taubah is their belief or commandment to avoid them like najis and not that their bodies are najis. 
As for the issue of physical contact with non-Muslims – there is concern that there is a possibility they held a najis beforehand – then in this matter, there is an Islamic legal maxim that states:
نَحْنُ نَحْكُمُ بِالظَّاهِرِ، وَاللهُ يَتَوَلَّى السَّرَائِرَ
“We rule based on what we see and Allah will manage what is hidden.” 
Thus, basically, it is unnecessary to wash any of our body parts that came into contact with their bodies as long as there is no evidence that shows that they held any najis beforehand or there aren’t any signs or traces of the najis such as saliva and others.
According to the above discussion, we conclude that a non-Muslim is not considered as najis. As for the uncleanliness referred to them is in regards to their deviated belief and not physical najis.
Likewise, when one comes into physical contact with a non-Muslim, even if the non-Muslim keeps a dog, it is unnecessary to wash oneself except if one touches him and he had just touched his dog and there are traces or signs of him touching his dog, such as the dog’s saliva and others. In this matter, we hold unto what is clearly seen and hands over the unseen to Allah SWT.
May Allah SWT grants us all a clear understanding in religion. Amin.