Jeppesen SIDs are designed with a "Procedural Design Gradient" consisting of 2.5% of "Obstacle Identification Surface" plus 0.8% of "Increasing Obstacle Clearance" = 3.3%.
If no obstacles are a factor with this 3.3%, that is your SID minimum climb gradient. However, if obstacles require a gradient in excess of this, then additional required gradient information will be published on the SID chart itself - usually in a statement of words format & a table. For example, you may see something like "Runway 18: 3.5% required" or "Runway 09 - 630 ft per nm required" and a table giving the required rate of climb vs groundspeed.
As i mentioned, you only see this information whenever an excess of 3.3% is required; if you don't see anything on the chart, then 3.3% is your minimum climb gradient.