> In which DLL are the isc_action_svc_trace_* functions located? I am

> planning to call it from a Lazarus project

  As i already wrote, you should work with Services API. If you never works with it before i suggest to
read IB6 "API Guide"

https://www.firebirdsql.org/en/reference-manuals/

and corresponding docs for Lazarus access components you used to work with Firebird.

isc_action_svc_trace_* is not a functions exported from DLL.
This is numeric constants (tags) used to work with Services API.

Hope it helps,
Vlad

PS avoid overquoting, please