A tahir thing becomes najis if it comes in contact with a najis thing with dampness.

Yes, it does become najis.

Yes, the whole bathroom floor becomes najis in the said scenario with the existence of dampness, and whatever touches it with dampness becomes najis, provided that this was the only cleaning method used.
If the floor is cleaned through other ways as well in which the taharah of the floor is achieved, such as with running tap water, such that one is no longer certain of the najasah of the floor when it comes in contact with the foot or the clothes, then one can consider the foot as tahir.
This applies to any situation where najasah is doubted after being sure that taharah took place.

All the mentioned things are considered as najis if the contact was with dampness.

The part of the body and clothing that came in contact with urine becomes najis, and whatever comes in contact with the najis body or clothing with transferring dampness also becomes najis. So, if the sweat transfers the wetness from the najis body or clothing to anything else, the latter also becomes najis.

Object D is considered as najis and can cause other things to become najis as well when contacted with dampness.

In the event that the urine or semen is not seen on the bed or blanket, if the dampness of the najasah is transferred to the bed or the blanket, then the bed or blanket becomes najis as well. If not then the bed or blanket is not najis.

As long as the moisture is present between two objects, the najasah will transfer, however many times this may happen. There is no maximum number of transfers.

This does not make everything najis, since one is not aware that they had been in contact with najis things with dampness, or one is sure that a particular thing became tahir and najis without knowing which one was first. In such cases it is considered to be tahir.

As long as you are not sure that your hand was najis when you touched the mobile phone, you can consider it as tahir. Furthermore, najasah is transferred from one thing to another if the dampness in one of them is transferred to the other. If the mobile phone does become najis, then it cannot be purified again except with water. It is not prohibited to use it while it is najis.

He is not considered to be najis. Only whatever came in contact with the wine is considered to be najis.

If you know it to be semen or najis liquid, the bedding will become najis, but as long as it is dry the najasah will not transfer to something else.

If one piece of clothing is najis, then washing it with tahir clothes makes all clothes being washed najis even if detergent is used. They do not become tahir again unless they were washed with unmixed tahir water.

The hand does not become najis in the prescribed scenario.

Having sexual intercourse with your wife makes you in the state of janābah. It does not make your body najis. It makes the parts of your body that were in contact with semen najis only. If you made these parts tahir after the intercourse ends, then the entirety of your body is tahir. However, you are still required to perform the ghusl of janābah before offering the prayers. Therefore, you do not need to wash your clothes simply because you wore them when you were in the state of janābah, unless the semen or any other najasah came in contact with them.

If you have a doubt about whether the wet hair touched and blood stain, and there is a possibility in your mind that the hair could have avoided contact with the blood, then the principle of taharah applies here. This principle states a thing does not become najis unless you know that it has made contact with najasah and it has transferred.