In an SLD styling file for a line geometry, you can use a PointSymbolizer in combination with the geometry function vertices to style the points of the line.

Program: Defining a line style and a point style for the points of a line
<?xml version='1.0' encoding='UTF-8'?>
<FeatureTypeStyle xmlns="http://www.opengis.net/se"
                  xmlns:ogc="http://www.opengis.net/ogc"
                  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                  xsi:schemaLocation="http://www.opengis.net/se http://schemas.opengis.net/se/1.1.0/FeatureStyle.xsd http://www.opengis.net/ogc http://schemas.opengis.net/filter/1.1.0/filter.xsd"
                  version="1.1.0">
  <Rule>
    <Name>Line_With_Point_Styling</Name>
    <LineSymbolizer>
      <Stroke>
        <SvgParameter name="stroke">#0000FF</SvgParameter>
        <SvgParameter name="stroke-width">2</SvgParameter>
      </Stroke>
    </LineSymbolizer>
    <PointSymbolizer>
      <Geometry>
        <ogc:Function name="vertices"/>
      </Geometry>
      <Graphic>
        <Mark>
          <WellKnownName>circle</WellKnownName>
          <Fill>
            <SvgParameter name="fill">#0000FF</SvgParameter>
            <SvgParameter name="fill-opacity">0.5</SvgParameter>
          </Fill>
          <Stroke>
            <SvgParameter name="stroke">#0000FF</SvgParameter>
            <SvgParameter name="stroke-width">2</SvgParameter>
          </Stroke>
        </Mark>
        <Size>30</Size>
      </Graphic>
    </PointSymbolizer>
  </Rule>
</FeatureTypeStyle>