To find the 12th term of the arithmetic sequence $U_n=2,6,10,\dots$, we use the formula for the $n$-th term of an arithmetic sequence:

$$U_n=U_1+(n-1)\times d$$

where:
- $U_1$ is the first term,
- $d$ is the common difference,
- $n$ is the term number.

From the sequence:
- The first term $U_1=2$,
- The common difference $d=6-2=4$.

We need to find the 12th term $U_{12}$:

1. Substitute the values into the formula:

$$U_{12}=2+(12-1)\times 4$$

2. Calculate:

$$U_{12}=2+11\times 4$$
$$U_{12}=2+44$$
$$U_{12}=46$$

The 12th term of the sequence is 46.

The correct answer is A. 46