Do not use the ConfigAdmin directly, I would consider this an Antipattern. A service/component should only read its own properties, but not read the property of other services, these are typically implementation details. If you really need to know something about other services, extend their interface and provide the information via the public API of this service. Then the compiler can support you to write robust code.
To read values of config, you need to get reference of ConfigurationAdmin which is only possible if your class is an OSGi component. If there is a helper class where you want to read such properties, you need to pass ConfigurationAdmin object to that method and then read the properties.