Please see the steps below to have the high point markers:
Step 1: Select any cell with line sparklines (please check how to insert sparklines);
Step 2: Click the "Design" tab from the Ribbon;
Step 3: Check the "High Point" in the "Show" section;
Step 4: Select one style from the "Style" section;
Alternatively, you define the sparkline and marker color by using the "Sparkline Color" and the "Marker Color".
Step 5: To change the "High Point" color, click the "Marker Color";
Step 6: Click the "High Point" command from the drop-down list and select a color from the theme color;
Step 7: You can also change many other components such as the low point, first or last point, etc.