Do I need ISO 17025 certification in order to audit laboratories?

You asked

as a lab expert, do I also need ISO17025 certification in order to audit laboratories? Or is 9001 is sufficient?

 
There are very few options to obtain ISO 17025 auditing certification. As ISO 9001 is incorporated into the ISO 17025:2017 Management requirements and ISO 17025 Lead Auditor certification courses may not be as readily available, the ISO 9001:2015 Lead Auditor Training Course is a good option. (see https://advisera.com/training/iso-9001-lead-auditor-course/)
There are two components to auditing to consider:

• Auditing skills - Training should include exposure /introduction to ISO 19011: Guidelines for Auditing Management Systems as it is provides guidelines for auditing all management systems.
• Knowledge of the standard against which you are auditing. 

Auditing basics, roles and the principles of auditing covered in the ISO 9001 auditing course will be applicable to auditing ISO 17025 as well. In ISO 17025 auditing the lead auditor should have appropriate auditing skills to assess the management clauses, meaning all those that do not have a technical component. The technical auditor also needs to also have appropriate auditing skills but must also have the ability to audit the technical aspects, including method validation and measurement uncertainty, quality control. In other words the depth of knowledge and skill to delve deep enough into the risks and assess technical validity and competency. This experience comes from hands on working in a laboratory and attending additional training on technical matters. Based on your comments, this is experience you have.

If you choose to obtain ISO 17025:2017 Lead Auditor certification; select a suitable course offered by an approved Training Partners of an international certification body such as Exemplar Global (formally RABQSA) or IRCA (The International Register of Certificated Auditors). 

Have a look at Advisera’s Certification FAQs at https://advisera.com/training/eu-gdpr-courses/ for further information regarding certification