<showDeprecation>
Sets whether to show source locations where deprecated APIs are used.

• Default value is: false
• User property is: maven.compiler.showDeprecation

<showWarnings>
Set to true to show compilation warnings.

• Default value is: false
• User property is: maven.compiler.showWarnings

-- Maven Doku

As simple as mvn clean install -Dmaven.compiler.showDeprecation=true -Dmaven.compiler.showWarnings=true all in one line.

You could even remove the =true part because, when you add a maven parameter with -D it automatically sets its value to true, if not set to something else.

With maven 3.3.9, using the maven-compiler-plugin and Java 1.8, you need a <configuration> section like the following:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.8.0</version>
    <executions>
        <execution>
            <id>compile</id>
            <phase>compile</phase>
            <goals>
                <goal>compile</goal>
            </goals>
        </execution>
        <execution>
            <id>testCompile</id>
            <phase>test-compile</phase>
            <goals>
                <goal>testCompile</goal>
            </goals>
        </execution>
    </executions>
    <configuration>
        <compilerArgument>-Xlint:all</compilerArgument>
        <showWarnings>true</showWarnings>
        <showDeprecation>true</showDeprecation>
    </configuration>
</plugin>

I got this answer from here when none of the above worked for me: http://frequal.com/java/EnableWarningsInMaven.html

I am guessing you are using the compiler plugin. Have you tried this?