The mode of the observations 23, 26, 15, 12, 28, 38, 19, 23, 26, 23 is 28.

Answer

To find the mode of the observations 23, 26, 15, 12, 28, 38, 19, 23, 26, 23, we will follow these steps:

### Step 1: List the Observations
We start by writing down all the observations given in the question:
- 23, 26, 15, 12, 28, 38, 19, 23, 26, 23

### Step 2: Count the Frequency of Each Observation
Next, we will count how many times each number appears in the list:
- 12 appears 1 time
- 15 appears 1 time
- 19 appears 1 time
- 23 appears 3 times
- 26 appears 2 times
- 28 appears 1 time
- 38 appears 1 time

### Step 3: Identify the Mode
The mode is the number that appears most frequently in the data set. From our frequency count:
- 23 appears 3 times, which is more than any other number.

### Conclusion
Thus, the mode of the observations is **23**.