How can I generalize the arity of rxjava2 Zip function (from Single/Observable) to n Nullable arguments without lose its types?

A function with eleven parameters is a good example for unclean code. Instead you should consider to build a model to serve your needs. Like this you can provide meaningful names for each argument as well.

data class MyObject(...)

class MyMutableObject {
    private lateinit var param0: String
    private var param1: Int
    ...

    fun setParam0(value: String) {
        param0 = value
    }
    fun setParam1(value: Int) {
        param1 = value
    }
    ...

    fun toMyObject() = MyObject(
        param0,
        param1,
        ...
    ) 
}

Having this model you could just use the zipWith() operator on each of your sources.

Single.just(MyMutableObject())
      .zipWith(source0, MyMutableObject::setParam0)
      .zipWith(source1, MyMutableObject::setParam1)
      ...
      .map(MyMutableObject::toMyObject)

If you consider to abstract the nullability as a Maybe, you could simply define an extension function receiving a Maybe with data or without data and map it appropriately.

inline fun <T, U, R> Single<T>.zipWith(
        other: MaybeSource<U>,
        crossinline zipper: (T, U) -> R
) = other.zipWith(toMaybe()) { t, u -> zipper(t, u) }
         .switchIfEmpty(this)